{"product_id":"fish-pen","title":"Fish Pen (Fix Pen) 500mg 30\/60ct","description":"\u003cstyle\u003e\n  html:has(.fph-product-copy) {\n    scroll-behavior: auto;\n  }\n  @media (prefers-reduced-motion: no-preference) {\n    html:has(.fph-product-copy) {\n      scroll-behavior: smooth;\n    }\n  }\n\n  .fph-product-copy {\n    --fph-text: #1f2937;\n    --fph-heading: #111827;\n    --fph-border: #d9dde6;\n    --fph-surface: #f8fafc;\n    --fph-surface-alt: #f3f5f8;\n    --fph-accent: #143583;\n    --fph-danger: #c62828;\n    --fph-warning: #f59e0b;\n    --fph-radius: 18px;\n    color: var(--fph-text);\n    font-size: clamp(15px, 1.05vw, 17px);\n    line-height: 1.75;\n    overflow-wrap: break-word;\n  }\n\n  .fph-product-copy,\n  .fph-product-copy * {\n    box-sizing: border-box;\n  }\n\n  .fph-product-copy .fph-section \u003e * + *,\n  .fph-product-copy .fph-panel \u003e * + * {\n    margin-top: clamp(14px, 2vw, 20px);\n  }\n\n  .fph-product-copy h2 {\n    margin: 0;\n    color: 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class=\"fph-product-copy\"\u003e\n\u003csection id=\"overview\" class=\"fph-section\"\u003e\n\u003ch2\u003eFix Pen (Fish Pen Forte) Penicillin Tablets - 500 mg\u003c\/h2\u003e\n\u003cnav class=\"fph-toc\" aria-label=\"On this page\"\u003e\u003cspan class=\"fph-toc-label\"\u003eOn this page:\u003c\/span\u003e \u003ca href=\"#overview\"\u003eOverview\u003c\/a\u003e \u003ca href=\"#fish-pen-vs-fix-pen\"\u003eFish Pen vs Fix Pen\u003c\/a\u003e \u003ca href=\"#benefits\"\u003eBenefits\u003c\/a\u003e \u003ca href=\"#dosage\"\u003eUsage\u003c\/a\u003e \u003ca href=\"#mechanism\"\u003eHow It Works\u003c\/a\u003e \u003ca href=\"#side-effects\"\u003eSafety\u003c\/a\u003e \u003ca href=\"#shipping\"\u003eShipping\u003c\/a\u003e \u003ca href=\"#faq\"\u003eFAQ\u003c\/a\u003e\u003c\/nav\u003e\n\u003ctable class=\"fph-spec-table\"\u003e\n\u003ccaption\u003eFix Pen at a Glance\u003c\/caption\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth scope=\"row\"\u003eFor\u003c\/th\u003e\n\u003ctd\u003eOrnamental aquarium fish and non-food pet birds\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth scope=\"row\"\u003eHelps with\u003c\/th\u003e\n\u003ctd\u003eSuspected bacterial problems such as fin rot, tail rot, ulcers and pop-eye\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth scope=\"row\"\u003eForm\u003c\/th\u003e\n\u003ctd\u003eTablets, 500 mg each\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth scope=\"row\"\u003eCount sizes\u003c\/th\u003e\n\u003ctd\u003e30 count, 60 count\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth scope=\"row\"\u003eWater type\u003c\/th\u003e\n\u003ctd\u003eFreshwater and saltwater\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth scope=\"row\"\u003eMade in\u003c\/th\u003e\n\u003ctd\u003eUnited States by Aqua Soma Labs\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp\u003e\u003cstrong\u003eFix Pen\u003c\/strong\u003e is an antibacterial treatment for ornamental aquarium fish and non-food pet birds. Each tablet contains 500 mg of Penicillin V Potassium, made by Aqua Soma Labs in the United States and sold in bottles of 30 or 60 tablets with fresh expiration dates.\u003c\/p\u003e\n\u003cp\u003eAquarists may know this product as Fish Pen, Fish Pen Forte, Aqua Pen or FISHBIOTIC Penicillin. Those were Thomas Labs brand names, and Fix Pen is the current replacement now that the Thomas Labs line is discontinued. Keepers usually reach for penicillin tablets for fish when they see fin rot, tail rot, infected wounds, pop-eye (bulging eyes) or columnaris-type lesions, sometimes called cotton-wool disease, where a bacterial cause is suspected.\u003c\/p\u003e\n\u003cp\u003ePenicillin V works on the cell walls of certain bacteria and can stop certain gram-positive bacteria from multiplying. Fix Pen is the fish penicillin 500 mg tablet many hobbyists use for fish tank infections, and the same tablets are used as penicillin for birds under avian veterinary guidance. It targets gram-positive and some gram-negative bacteria in ornamental aquarium use.\u003c\/p\u003e\n\u003cp\u003eEach tablet contains 500 mg, and bottles come in 30 or 60 tablets. The 30-count suits a single hospital tank or occasional use; the 60-count fits multi-tank setups or aviary needs. You can buy Fix Pen online with fresh expiration dates and U.S. shipping.\u003c\/p\u003e\n\u003cp\u003eStart treatment early, at the first signs of a suspected bacterial problem. The signs are not the same for fish and birds, so use the lists below to know what to watch for.\u003c\/p\u003e\n\u003cdiv class=\"fph-info-grid\"\u003e\n\u003cdiv class=\"fph-info-card\"\u003e\n\u003ch3\u003eFish-Specific Symptoms\u003c\/h3\u003e\n\u003cul class=\"fph-symptom-list\"\u003e\n\u003cli\u003eFin and tail rot (frayed or rotting fins)\u003c\/li\u003e\n\u003cli\u003eMouth rot and infected wounds\u003c\/li\u003e\n\u003cli\u003ePop-eye (bulging eyes) or cloudy eyes\u003c\/li\u003e\n\u003cli\u003eColumnaris-type lesions (cotton-wool look)\u003c\/li\u003e\n\u003cli\u003eOpen sores, ulcers or reddening of the skin\u003c\/li\u003e\n\u003cli\u003eReduced appetite, lethargy or hiding\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"fph-info-card\"\u003e\n\u003ch3\u003eBird-Specific Symptoms (Under Veterinary Guidance)\u003c\/h3\u003e\n\u003cul class=\"fph-symptom-list\"\u003e\n\u003cli\u003eRespiratory infections with labored breathing\u003c\/li\u003e\n\u003cli\u003eSoft tissue infections where a vet suspects bacteria\u003c\/li\u003e\n\u003cli\u003eFluffed-up feathers, lethargy or inactivity\u003c\/li\u003e\n\u003cli\u003eDecreased appetite\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cp\u003eFor birds, only reach for Fix Pen when an avian veterinarian has recommended penicillin for a specific problem. Catching an infection early, paired with clean water and good husbandry, gives your fish and birds the best chance to recover.\u003c\/p\u003e\n\u003cp\u003eHusbandry still does most of the work. Stable water and good feeding prevent more problems than any treatment can fix. Penicillin does nothing for viral issues, and using fish treatments like penicillin when they are not needed can reduce how well they work later.\u003c\/p\u003e\n\u003cp class=\"fph-tip\"\u003e\u003cstrong\u003eOrder online:\u003c\/strong\u003e in-stock orders placed before 1:30 p.m. CT, Monday through Friday, ship the same day from our U.S. warehouse by USPS or UPS.\u003c\/p\u003e\n\u003cp class=\"fph-alert\"\u003e\u003cstrong\u003eImportant Notice:\u003c\/strong\u003e This product is \u003cstrong\u003eintended for aquarium and ornamental fish and pet birds only\u003c\/strong\u003e. It is \u003cstrong\u003enot for animals used for food\u003c\/strong\u003e.\u003c\/p\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003csection id=\"fish-pen-vs-fix-pen\" class=\"fph-section\"\u003e\n\u003ch2\u003eFish Pen Forte vs Fix Pen: What Changed?\u003c\/h2\u003e\n\u003cp\u003eIf you used Thomas Labs Fish Pen, Fish Pen Forte, Aqua Pen or FISHBIOTIC Penicillin, here is what is the same and what is different:\u003c\/p\u003e\n\u003cdiv class=\"fph-info-grid\"\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eSame Penicillin Formula\u003c\/strong\u003e Fix Pen contains the same 500 mg Penicillin V Potassium per tablet that you used in Fish Pen and Fish Pen Forte. The formula targets the same bacteria.\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eNew Manufacturer\u003c\/strong\u003e Fix Pen is made by Aqua Soma Labs, which replaced the discontinued Thomas Labs line. Aqua Soma Labs manufactures it in the United States.\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eSame Tablet Form\u003c\/strong\u003e Fix Pen uses the same tablet format as the original Fish Pen, so it is easy to dissolve in aquarium water or crush for precise dosing in a hospital tank.\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eAvailable in 30-Count and 60-Count Bottles\u003c\/strong\u003e Pick the size that fits your setup: a 30-count bottle for a single hospital tank or occasional use, or a 60-count bottle for larger collections, multi-tank operations or aviary needs.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003csection id=\"benefits\" class=\"fph-section\"\u003e\n\u003ch2\u003eBenefits of Fix Pen for Fish \u0026amp; Birds\u003c\/h2\u003e\n\u003cul class=\"fph-card-list\"\u003e\n\u003cli\u003e\n\u003ch3\u003eTargeted Gram-Positive Bacterial Coverage\u003c\/h3\u003e\n\u003cp\u003eA classic penicillin choice when a gram-positive bacterial component is suspected in ornamental fish, especially when the signs look like fin and tail rot, mouth rot, sores, pop-eye or cloudy eyes.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eMade in the USA with Fresh Dating\u003c\/h3\u003e\n\u003cp\u003eFix Pen is manufactured in the United States by Aqua Soma Labs and ships with fresh expiration dates, so you can keep a bottle on hand for your hospital tank and trust it when you need it.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eConsistent 500 mg Tablets\u003c\/h3\u003e\n\u003cp\u003eEach tablet delivers a reliable 500 mg dose of Penicillin V Potassium, so it is easy to scale from a single betta or quarantine tank to larger community aquariums.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eCommon Aquarium Use Cases\u003c\/h3\u003e\n\u003cp\u003eOften chosen when the goal is to target gram-positive and some gram-negative bacteria in ornamental fish. In aquarium care discussions, penicillin comes up for flexibacter-type issues, infected wounds and worsening fin damage when a bacterial component is suspected.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eFreshwater and Saltwater Compatible\u003c\/h3\u003e\n\u003cp\u003eMade for ornamental aquarium use in both freshwater and saltwater setups when used as directed. A separate hospital tank is still recommended when possible to protect the main display system.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eQuarantine-Friendly and Biofilter Aware\u003c\/h3\u003e\n\u003cp\u003ePenicillin may affect beneficial bacteria and can be risky for invertebrates like shrimp and snails. A separate treatment tank protects the main display and makes water-quality monitoring easier during treatment.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eIdeal for Hospital Tanks and Quarantine\u003c\/h3\u003e\n\u003cp\u003eTreating in a separate hospital tank keeps the main aquarium's biofilter intact and limits exposure for healthy tank mates, so you can focus the treatment where it is needed.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003csection id=\"dosage\" class=\"fph-section\"\u003e\n\u003ch2\u003eUsage Guidelines \u0026amp; Instructions\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eQuick usage summary for fish:\u003c\/strong\u003e Use \u003cstrong\u003e1 tablet per 20 gallons (76 L)\u003c\/strong\u003e, repeat every 24 hours, and do a partial water change between doses. Continue for \u003cstrong\u003e5 to 10 days\u003c\/strong\u003e, and stop if you see no improvement after 5 days.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDirections for Use:\u003c\/strong\u003e\u003c\/p\u003e\n\u003col class=\"fph-step-list\"\u003e\n\u003cli\u003e\n\u003ch3\u003eSet Up a Separate Treatment Area\u003c\/h3\u003e\n\u003cp\u003eWhen possible, treat fish in a hospital or quarantine tank. This limits exposure for healthy tank mates and makes it easier to watch results and water quality. Remove activated carbon and turn off UV sterilizers during treatment, since they can strip the penicillin from the water.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eDirections for Fish Aquariums\u003c\/h3\u003e\n\u003cp\u003eDissolve \u003cstrong\u003eone (1) 500 mg tablet\u003c\/strong\u003e in a small cup of aquarium water first, then add the dissolved dose for every \u003cstrong\u003e20 gallons (76 L)\u003c\/strong\u003e of water you are treating. Repeat every \u003cstrong\u003e24 hours\u003c\/strong\u003e, with a partial water change between treatments.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eDuration and When to Stop\u003c\/h3\u003e\n\u003cp\u003eContinue for \u003cstrong\u003e5 to 10 days\u003c\/strong\u003e. If you see no improvement after 5 days, stop and consider asking an aquatic professional about next steps. Finish the full recommended number of days even if the fish look better, since stopping early can let the problem come back.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eMaintain Water Quality During Treatment\u003c\/h3\u003e\n\u003cp\u003eKeep strong aeration and watch your water parameters, especially ammonia and nitrite. Because penicillin may affect beneficial bacteria and can be risky for invertebrates like shrimp and snails, a separate treatment tank and close observation are strongly recommended.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003ePet Birds (Under Veterinary Guidance Only)\u003c\/h3\u003e\n\u003cp\u003eFor non-food pet birds, use penicillin only under avian veterinary guidance for amount, frequency and duration. Your vet can advise the correct amount for the bird's weight and decide whether to treat a single bird or the whole flock.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003ctable class=\"fph-dose-table\"\u003e\n\u003ccaption\u003eFix Pen Amounts by Aquarium Size\u003c\/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth scope=\"col\"\u003eTank volume\u003c\/th\u003e\n\u003cth scope=\"col\"\u003ePenicillin per use\u003c\/th\u003e\n\u003cth scope=\"col\"\u003e500 mg tablets\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003e10 gallons (38 L)\u003c\/td\u003e\n\u003ctd\u003e250 mg\u003c\/td\u003e\n\u003ctd\u003ehalf a tablet (split)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e20 gallons (76 L)\u003c\/td\u003e\n\u003ctd\u003e500 mg\u003c\/td\u003e\n\u003ctd\u003e1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e40 gallons (151 L)\u003c\/td\u003e\n\u003ctd\u003e1000 mg\u003c\/td\u003e\n\u003ctd\u003e2\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e60 gallons (227 L)\u003c\/td\u003e\n\u003ctd\u003e1500 mg\u003c\/td\u003e\n\u003ctd\u003e3\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e75 gallons (284 L)\u003c\/td\u003e\n\u003ctd\u003eabout 1875 mg\u003c\/td\u003e\n\u003ctd\u003eabout 4\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp\u003eThese amounts follow the label guideline of one 500 mg tablet per 20 gallons (76 L), roughly 25 mg per gallon. Dose by the water volume of your treatment tank, not by the number of fish, give one dose every 24 hours for 5 to 10 days, and make a partial water change between doses. Splitting a tablet by hand is only approximate, so for tanks under 20 gallons it is better to dissolve a whole tablet in a measured cup of tank water and add the matching fraction. Continuing for the full recommended number of days matters as much as picking the right treatment. The bottle label or your aquatic veterinarian takes priority over this quick-reference chart.\u003c\/p\u003e\n\u003ch3\u003eWhat to Expect During Treatment\u003c\/h3\u003e\n\u003cdiv class=\"fph-info-grid\"\u003e\n\u003cdiv class=\"fph-info-card\"\u003e\n\u003ch3\u003eDays 1 to 2\u003c\/h3\u003e\n\u003cp\u003eFish may hide or eat less, and the water can look slightly cloudy. This is normal early on. Keep dosing on schedule and keep aeration strong.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"fph-info-card\"\u003e\n\u003ch3\u003eDays 3 to 5\u003c\/h3\u003e\n\u003cp\u003eLook for signs it is working: sores and red patches stop spreading, appetite starts to return, and breathing steadies. If there is no change by day 5, or the fish look worse, stop and ask an aquatic professional.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"fph-info-card\"\u003e\n\u003ch3\u003eDays 5 to 10\u003c\/h3\u003e\n\u003cp\u003eEven if the fish are improving, finish the full treatment so the infection does not return. Afterward, run a partial water change and put activated carbon back in to clear any leftover penicillin.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cfigure class=\"fph-figure\"\u003e\n\u003csvg viewbox=\"0 0 760 185\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" role=\"img\" aria-labelledby=\"fixpen-tl-title fixpen-tl-desc\"\u003e\n\u003ctitle id=\"fixpen-tl-title\"\u003eFix Pen treatment timeline\u003c\/title\u003e\n\u003cdesc id=\"fixpen-tl-desc\"\u003eA typical Fix Pen treatment for aquarium fish runs 5 to 10 days. Days 1 to 2: set up and start treatment. Days 3 to 5: watch for response. Day 5: reassess and stop if there is no improvement. Days 5 to 10: finish the treatment.\u003c\/desc\u003e\n\u003ctext x=\"150\" y=\"34\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"15\" font-weight=\"700\" fill=\"#111827\"\u003eDays 1 to 2\u003c\/text\u003e\n\u003ctext x=\"150\" y=\"56\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"13\" fill=\"#475569\"\u003eSet up \u0026amp; start\u003c\/text\u003e\n\u003ctext x=\"370\" y=\"34\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"15\" font-weight=\"700\" fill=\"#111827\"\u003eDays 3 to 5\u003c\/text\u003e\n\u003ctext x=\"370\" y=\"56\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"13\" fill=\"#475569\"\u003eWatch for response\u003c\/text\u003e\n\u003ctext x=\"600\" y=\"34\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"15\" font-weight=\"700\" fill=\"#111827\"\u003eDays 5 to 10\u003c\/text\u003e\n\u003ctext x=\"600\" y=\"56\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"13\" fill=\"#475569\"\u003eFinish the treatment\u003c\/text\u003e\n\u003crect x=\"40\" y=\"86\" width=\"220\" height=\"16\" rx=\"8\" fill=\"#143583\"\u003e\u003c\/rect\u003e\n\u003crect x=\"262\" y=\"86\" width=\"216\" height=\"16\" rx=\"8\" fill=\"#4a6fb5\"\u003e\u003c\/rect\u003e\n\u003crect x=\"480\" y=\"86\" width=\"240\" height=\"16\" rx=\"8\" fill=\"#9fb3d9\"\u003e\u003c\/rect\u003e\n\u003ccircle cx=\"40\" cy=\"94\" r=\"10\" fill=\"#143583\" stroke=\"#ffffff\" stroke-width=\"3\"\u003e\u003c\/circle\u003e\n\u003ccircle cx=\"480\" cy=\"94\" r=\"10\" fill=\"#f59e0b\" stroke=\"#ffffff\" stroke-width=\"3\"\u003e\u003c\/circle\u003e\n\u003ccircle cx=\"720\" cy=\"94\" r=\"10\" fill=\"#9fb3d9\" stroke=\"#ffffff\" stroke-width=\"3\"\u003e\u003c\/circle\u003e\n\u003ctext x=\"40\" y=\"132\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"14\" font-weight=\"700\" fill=\"#111827\"\u003eDay 1\u003c\/text\u003e\n\u003ctext x=\"480\" y=\"132\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"14\" font-weight=\"700\" fill=\"#111827\"\u003eDay 5\u003c\/text\u003e\n\u003ctext x=\"720\" y=\"132\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"14\" font-weight=\"700\" fill=\"#111827\"\u003eDay 10\u003c\/text\u003e\n\u003ctext x=\"480\" y=\"154\" text-anchor=\"middle\" font-family=\"inherit\" font-size=\"12\" fill=\"#c62828\"\u003ereassess; stop if no improvement\u003c\/text\u003e\n\u003c\/svg\u003e\n\u003cfigcaption\u003eFix Pen treatment timeline: a typical 5 to 10 day treatment for aquarium fish, with a reassessment point at day 5.\u003c\/figcaption\u003e\n\u003c\/figure\u003e\n\u003cdiv class=\"fph-info-card\"\u003e\n\u003ch3\u003eWhat You Need for Treatment\u003c\/h3\u003e\n\u003cp\u003eA little setup before the first dose saves trouble later.\u003c\/p\u003e\n\u003cul class=\"fph-symptom-list\"\u003e\n\u003cli\u003eA separate hospital or quarantine tank, so you are not treating the whole display.\u003c\/li\u003e\n\u003cli\u003eA heater and an air stone or sponge filter for steady temperature and strong aeration.\u003c\/li\u003e\n\u003cli\u003eAn ammonia and nitrite test kit to keep tabs on water quality.\u003c\/li\u003e\n\u003cli\u003eA dechlorinator for the water changes between doses.\u003c\/li\u003e\n\u003cli\u003eA small net and a clean cup for gentle transfer and measuring the dose.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cp class=\"fph-tip\"\u003e\u003cstrong\u003ePro Tip:\u003c\/strong\u003e Dose by the actual treated water volume, not the tank's advertised size, since gravel, decorations and equipment reduce usable volume. Daily observation and stable water quality matter as much as the dose.\u003c\/p\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003csection id=\"mechanism\" class=\"fph-section\"\u003e\n\u003ch2\u003eHow Fix Pen Works\u003c\/h2\u003e\n\u003cp\u003eEach Fix Pen tablet contains 500 mg of Penicillin V Potassium, a penicillin that acts on the cell walls of certain bacteria. It helps control certain gram-positive bacteria, and some gram-negative bacteria, when used as directed in ornamental fish care.\u003c\/p\u003e\n\u003cp\u003eThe rest of each tablet is made up of standard ingredients that hold it together on the shelf and let it break apart and dissolve when you add it to aquarium water or a treatment setup.\u003c\/p\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003cdiv id=\"side-effects\" class=\"fph-panel\"\u003e\n\u003ch2\u003eSafety and Tank Notes\u003c\/h2\u003e\n\u003cp\u003eWhen used as directed, Fix Pen usually causes no problems in ornamental fish. As with any treatment, unnecessary use, incorrect amounts or combining products can stress fish and reduce how well it works next time.\u003c\/p\u003e\n\u003cul class=\"fph-card-list\"\u003e\n\u003cli\u003e\n\u003ch3\u003eFish\u003c\/h3\u003e\n\u003cp\u003eSome fish may show short-term stress, reduced appetite or hiding during treatment. If you notice severe distress such as rapid gill movement, loss of balance, gasping at the surface or fish lying on the bottom, stop treatment, improve aeration, do a partial water change and seek aquatic veterinary or professional guidance.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eBirds\u003c\/h3\u003e\n\u003cp\u003eFor non-food pet birds, use penicillin only under avian veterinary guidance. If your bird becomes unusually lethargic, stops eating or seems unwell, stop use and contact your avian veterinarian.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eInvertebrates\u003c\/h3\u003e\n\u003cp\u003eDo not use Fix Pen in display tanks that hold shrimp, snails or other invertebrates, since penicillin may harm them or disrupt the tank. Whenever possible, move affected fish to a separate hospital tank.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eSafe use in your system\u003c\/h3\u003e\n\u003cp\u003eTreat fish in a hospital or quarantine tank whenever you can, remove activated carbon and turn off UV sterilizers during treatment, and watch ammonia, nitrite and temperature closely. Do not mix Fix Pen with other treatments unless a veterinarian advises it.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ch3\u003eImportant safety note\u003c\/h3\u003e\n\u003cp\u003eFix Pen is intended for \u003cstrong\u003eornamental aquarium fish and non-food pet birds only\u003c\/strong\u003e. \u003cspan class=\"fph-inline-warning\"\u003eIt is not for animals raised for food.\u003c\/span\u003e Store tablets in a cool, dry place away from direct sunlight, and keep them out of reach of children and pets. Always follow the directions on the label.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003chr\u003e\n\u003csection id=\"shipping\" class=\"fph-section\"\u003e\n\u003ch2\u003eShipping \u0026amp; Returns\u003c\/h2\u003e\n\u003cdiv class=\"fph-info-grid\"\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eShipping Policy:\u003c\/strong\u003e Orders ship from our U.S. warehouse within 1 business day via USPS or UPS, with same-day dispatch on in-stock orders placed before 1:30 p.m. CT (Monday through Friday). For full shipping details, please see our \u003ca href=\"https:\/\/finepethealth.com\/policies\/shipping-policy\"\u003eshipping policy\u003c\/a\u003e.\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eRefund Policy:\u003c\/strong\u003e If there is an issue with your order, you may be able to return or exchange items within 30 days according to our store guidelines. Before sending anything back, please review our \u003ca href=\"https:\/\/finepethealth.com\/policies\/refund-policy\"\u003erefund policy\u003c\/a\u003e carefully.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003csection id=\"faq\" class=\"fph-section\"\u003e\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003cdiv class=\"fph-faq-list\"\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eWhat is Fix Pen used for?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eFix Pen is a fish penicillin tablet (500 mg) used to help manage suspected bacterial problems in ornamental aquarium fish, especially gram-positive infections such as fin rot, tail rot, infected wounds, pop-eye and columnaris-type lesions. For non-food pet birds, use penicillin only under avian veterinary guidance for usage and treatment decisions.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eWhat is the difference between Fish Pen Forte and Fix Pen?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eFish Pen and Fish Pen Forte were brand names used by Thomas Labs for their penicillin tablets for fish. After Thomas Labs discontinued these products, Aqua Soma Labs introduced Fix Pen as a direct replacement. Fix Pen contains the same 500 mg Penicillin V Potassium per tablet and is intended for the same ornamental fish and pet bird uses.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eIs Fix Pen a replacement for FISHBIOTIC Penicillin or Aqua Pen?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eYes. If you previously used FISHBIOTIC Penicillin, Aqua Pen or any other 500 mg penicillin tablet for fish, Fix Pen from Aqua Soma Labs is a direct replacement with the same penicillin, 500 mg of Penicillin V Potassium per tablet, available in 30-count and 60-count bottles.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eHow soon should I see improvement with Fix Pen?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eMany keepers start to see early signs of a response by days 3 to 5, such as sores and red patches that stop spreading and appetite that begins to return. If there is no change by day 5, or the fish look worse, stop treatment and ask an aquatic professional about next steps. Finish the full treatment if the fish are improving.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eWhere can I buy penicillin tablets for fish online?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eYou can buy Fix Pen, a fish penicillin 500 mg tablet, directly from Fine Pet Health. We ship penicillin for fish and birds from our U.S. warehouse with same-day dispatch on in-stock orders placed before 1:30 p.m. CT, Monday through Friday, by USPS or UPS.\u003c\/p\u003e\n\u003ca rel=\"noopener\" href=\"https:\/\/finepethealth.com\/collections\/fish-and-bird-antibacterials\" class=\"fph-faq-link\"\u003eBrowse Fish \u0026amp; Bird Treatments Collection →\u003c\/a\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eWhat is in each Fix Pen tablet?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eEach Fix Pen tablet contains \u003cstrong\u003e500 mg Penicillin V Potassium\u003c\/strong\u003e. Penicillin V works by interfering with bacterial cell wall formation, which helps control certain gram-positive bacteria when used as directed.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eWhat is the Fix Pen amount for fish?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eFollow the label directions: add \u003cstrong\u003eone (1) 500 mg tablet per 20 gallons (76 L)\u003c\/strong\u003e of water you are treating, repeat every 24 hours and make a partial water change between doses. Continue for \u003cstrong\u003e5 to 10 days\u003c\/strong\u003e and stop if you see no improvement after 5 days.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eHow long should I treat with Fix Pen?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eLabel directions recommend treating for at least 5 days but no more than 10 days. If there is no improvement after 5 days, stop and reassess husbandry and next steps with an aquatic professional.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eShould I treat in the main tank or a hospital tank?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eA separate hospital or quarantine tank is strongly recommended. Penicillin and similar treatments may affect beneficial bacteria and can be risky for shrimp, snails, corals and other invertebrates, so dosing a display tank or reef setup is generally not a good idea. A small, dedicated hospital tank with a heater, air stone and no substrate makes dosing and water changes easier.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eDo I need to remove activated carbon or turn off UV during treatment?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eYes. Activated carbon and some chemical filtration media can remove the penicillin from the water. Take them out during treatment and put them back afterward. Many keepers also switch off UV sterilizers during dosing to keep levels in the water steady.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eWill Fix Pen harm beneficial bacteria in the aquarium?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eIt can. Penicillin, like other antibacterial treatments, may affect beneficial filter bacteria if used in the main tank. Using a hospital tank, watching ammonia and nitrite and doing partial water changes helps protect the biofilter during treatment.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eCan Fix Pen be used in saltwater aquariums?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eYes. Fix Pen can be used in both freshwater and saltwater hospital tanks. Dissolve the tablet at the standard dose (one 500 mg tablet per 20 gallons) and keep salinity, temperature and water quality stable through the treatment.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eIs Fix Pen safe for betta fish and small aquariums?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eYes. Fix Pen can be used in small hospital tanks for bettas and other individual fish. Because bettas are often kept in tanks under 20 gallons, you may need to split a tablet to reach the correct dose (one 500 mg tablet per 20 gallons). Dissolve the portion in a small cup of tank water before adding it to the hospital tank.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eCan I use Fix Pen in a planted tank or with shrimp and snails?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eIt is generally considered compatible with most planted tanks, but penicillin may harm shrimp, snails and other invertebrates. When possible, move affected fish to a separate hospital tank to limit plant and biofilter exposure and to protect invertebrates.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eCan Fix Pen treat fungal, viral or parasitic infections?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eNo. Fix Pen is a penicillin that targets certain bacterial infections only. It does not work against fungi, viruses or parasites such as ich, flukes or worms. For fungal, parasitic or viral problems, work with an aquatic or avian veterinarian to choose the right treatment.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eCan I combine Fix Pen with other fish treatments?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eCombining different treatments, or mixing Fix Pen with antifungal or antiparasitic products, is generally not recommended unless an aquatic veterinarian advises it. Using several products at once can stress fish, cause unpredictable interactions and make it harder to tell which one is working.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eWhat should I do after finishing a Fix Pen treatment?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eAfter the last dose, run a partial water change and put activated carbon back in to clear any leftover penicillin from the water. Keep watching ammonia and nitrite for a few days, since the biofilter can take time to recover, and only move fish back to the main tank once they are stable.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eCan I use Fix Pen for dogs, cats or chickens?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eFix Pen is labeled for ornamental aquarium fish and non-food pet birds only. It is not formulated, tested or approved for dogs, cats, chickens or other mammals and food animals. If your dog or cat needs penicillin, a licensed veterinarian should recommend the correct product and amount for that species.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eCan I use Fix Pen as penicillin for pet birds?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eFix Pen contains Penicillin V Potassium, the same penicillin used in avian care, so it can serve as a penicillin for birds option. Bird amounts are different from fish amounts and depend on the species and body weight, so use bird penicillin only under the direction of an avian veterinarian who can confirm a bacterial infection and set the amount and duration. Fix Pen is intended for non-food pet birds, not poultry raised for meat or eggs.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails class=\"fph-faq-item\"\u003e\n\u003csummary\u003eHow should I store and dispose of Fix Pen tablets?\u003c\/summary\u003e\n\u003cdiv class=\"fph-faq-answer\"\u003e\n\u003cp\u003eStore tablets in their original container in a cool, dry place away from heat, moisture, children and pets. Check the expiration date before use. For disposal, follow your local guidance for safe household disposal.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003c\/div\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003csection id=\"bottom-line\" class=\"fph-section\"\u003e\n\u003ch2\u003eBottom Line\u003c\/h2\u003e\n\u003cp\u003eFix Pen is a fish penicillin 500 mg tablet (Penicillin V Potassium) for gram-positive bacterial problems in ornamental aquarium fish, and a vet-directed penicillin option for non-food pet birds. It is the current replacement for the discontinued Thomas Labs Fish Pen and Fish Pen Forte. Dose by water volume at one 500 mg tablet per 20 gallons, treat for 5 to 10 days in a hospital tank, and reassess at day 5. It will not help with fungal, viral or parasitic problems, and it is not for animals raised for food. If you are unsure whether the cause is bacterial, or you are treating a bird, talk to an aquatic or avian veterinarian first. Ready to start? Choose the size that fits your setup above, or compare the rest of the Fix line below.\u003c\/p\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003csection class=\"fph-section\"\u003e\n\u003ch2\u003eMore Fish \u0026amp; Bird Treatments\u003c\/h2\u003e\n\u003cdiv class=\"fph-info-grid\"\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Mox (Amoxicillin) 250\/500mg\u003c\/strong\u003e A treatment for fin rot, dropsy, ulcers and other bacterial infections. Available in 30-count and 100-count capsules. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-mox\"\u003eShop Fix Mox\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Zole (Metronidazole) 250\/500mg\u003c\/strong\u003e Targets anaerobic bacteria and protozoa, including Hexamita and hole-in-the-head, in ornamental fish. Available in 60-count bottles. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-zole\"\u003eShop Fix Zole\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Doxy (Doxycycline) 100mg\u003c\/strong\u003e A treatment for columnaris, respiratory infections and Mycoplasma in fish and birds. Available in 30-count and 60-count tablets. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-doxy\"\u003eShop Fix Doxy\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Zithro (Azithromycin) 250mg\u003c\/strong\u003e A treatment for fin rot, columnaris, gill disease and avian respiratory concerns. Available in 12-count and 30-count tablets. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-zithro\"\u003eShop Fix Zithro\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Cin (Clindamycin) 150mg\u003c\/strong\u003e A treatment commonly used for gram-positive bacterial infections, including skin and soft tissue concerns in ornamental fish. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-cin\"\u003eShop Fix Cin\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Sulfa (SMZ\/TMP) 960mg\u003c\/strong\u003e A combination treatment offering broad coverage against a range of bacterial infections in ornamental fish. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-sulfa\"\u003eShop Fix Sulfa\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Flex (Cephalexin) 250\/500mg\u003c\/strong\u003e A treatment for fin rot, ulcers and bacterial skin infections in fish and birds. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-flex\"\u003eShop Fix Flex\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eFix Flox (Ciprofloxacin) 500mg\u003c\/strong\u003e A treatment for gram-negative bacterial infections, including fin rot, ulcers, columnaris and septicemia in ornamental fish. \u003ca href=\"https:\/\/finepethealth.com\/products\/fish-flox\"\u003eShop Fix Flox\u003c\/a\u003e\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eBrowse all treatments\u003c\/strong\u003e Explore our complete \u003ca rel=\"noopener\" href=\"https:\/\/finepethealth.com\/collections\/fish-and-bird-antibacterials\"\u003e\u003cstrong\u003eFish \u0026amp; Bird Treatments Collection\u003c\/strong\u003e\u003c\/a\u003e for more Fix line products and related care.\u003c\/p\u003e\n\u003cp class=\"fph-info-card\"\u003e\u003cstrong\u003eGuides and care tips\u003c\/strong\u003e Visit the \u003ca rel=\"noopener\" href=\"https:\/\/finepethealth.com\/blogs\/fish-and-bird-antibacterials\"\u003e\u003cstrong\u003eFish \u0026amp; Bird Care Blog\u003c\/strong\u003e\u003c\/a\u003e for practical dosing guides, water-care advice and treatment tips.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/section\u003e\n\u003chr\u003e\n\u003c\/div\u003e","brand":"Aqua Soma Labs","offers":[{"title":"500-mg (30 Count)","offer_id":49079636394234,"sku":"641664","price":35.3,"currency_code":"USD","in_stock":false},{"title":"500-mg (60 Count)","offer_id":49079636427002,"sku":"811294","price":69.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0655\/5244\/9786\/files\/fish-pen-penicillin-500mg-30-count-fish-antibacterial..webp?v=1782495908","url":"https:\/\/finepethealth.com\/products\/fish-pen","provider":"Fine Pet Health","version":"1.0","type":"link"}