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Fish Sulfa (Sulfamethoxazole Trimethoprim) 960mg 30 Count - Fish Treatment for Fungal and Bacterial Issues
Fish Sulfa (Sulfamethoxazole Trimethoprim) 960mg 60 Count - Remedy for Furunculosis in Ornamental Fish
Fish Sulfa (Sulfamethoxazole Trimethoprim) 960mg 30 Count - Fish Treatment for Fungal and Bacterial Issues
Fish Sulfa (Sulfamethoxazole Trimethoprim) 960mg 60 Count - Remedy for Furunculosis in Ornamental Fish

Fish Sulfa (Fix Sulfa) SMZ/TMP 960mg Fish Antibacterial

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Sulfamethoxazole and Trimethoprim for Fish: Fin Rot, Columnaris and Skin Ulcers in Freshwater and Saltwater Tanks

Fish Sulfa (Fix Sulfa) is an SMZ/TMP antibacterial treatment for ornamental aquarium fish, pairing sulfamethoxazole 800 mg with trimethoprim 160 mg per 960 mg tablet. Aquarists use it for fin and tail rot, columnaris, skin ulcers, and pop-eye in both freshwater and saltwater aquariums, including problems that are often linked to gram-negative bacteria such as Aeromonas and Pseudomonas. The label amount is one 960 mg tablet per 40 gallons (151 L) of water, repeated every 24 hours for 5 to 10 days.

In older hobby listings and aquarium forums, this SMZ/TMP product also goes by Fish Sulfa, Fish Sulfa Forte, FISHBIOTIC SMZ/TMP, and Aqua Sulfa. Fix Sulfa is the current-production replacement for the discontinued Thomas Labs Fish Sulfa Forte. Aquarists use this combination for fin and tail rot, columnaris (often presenting as cotton wool disease), skin sores and ulcer-like lesions, bacterial hemorrhagic septicemia, pop-eye (exophthalmia), cloudy eyes, and body slime issues linked to certain bacteria such as Aeromonas, Vibrio, or Streptococcus. Some keepers also search for it as fish bactrim or bactrim for fish, since Bactrim is another name for the sulfamethoxazole and trimethoprim combination.

Start treatment at the first signs of bacterial stress, and treat affected fish in a hospital or quarantine tank whenever possible. Watch for the symptoms below.

Important Notice: This product is intended for aquarium and ornamental fish only. It is not for animals used for food.

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SMZ/TMP pairs two ingredients that work together to help slow the growth of certain bacteria. Used as directed for fish, sulfamethoxazole and trimethoprim work best alongside stable water parameters, strong aeration, and good husbandry. Fix Sulfa is the current-production version.

Fish Symptoms Aquarists Treat With Fix Sulfa

  • Fin and tail rot (frayed or rotting fins)
  • Skin sores, ulcer-like lesions, and red streaks
  • Pop-eye (bulging eyes) and cloudy eyes
  • Columnaris, often with a cotton wool look
  • Bacterial hemorrhagic septicemia and body slime issues
  • Lethargy, rapid breathing, or loss of appetite that clean water does not fix

Fix Sulfa comes as a consistent 960 mg tablet that is easy to crush and dissolve. You can buy it online in bottles of 30 or 60 tablets with fresh expiration dates, so you can match the amount to a single quarantine tank or a multi-tank fish room.

Order before 1:30 p.m. CT, Monday through Friday, for same-day dispatch. Fix Sulfa ships from our U.S. warehouse via USPS or UPS.

Fish Sulfa Forte vs Fix Sulfa: What Changed?

If you previously purchased Thomas Labs Fish Sulfa Forte, FISHBIOTIC SMZ/TMP or Aqua Sulfa, here is what has changed and what remains the same:

Same Two Ingredients Fix Sulfa contains sulfamethoxazole 800 mg and trimethoprim 160 mg per tablet (SMZ/TMP 960 mg), the same dual-ingredient formula found in legacy products like Thomas Labs Fish Sulfa Forte, FISHBIOTIC SMZ/TMP, and Aqua Sulfa.

Updated Branding Aqua Soma Labs makes Fix Sulfa as a current-production replacement for the discontinued Thomas Labs Fish Sulfa Forte and other legacy SMZ/TMP fish treatments. The two ingredients and intended use are the same.

Same Tablet Form Each tablet delivers a consistent 960 mg in a format that is easy to crush and dissolve for aquarium use, following the same scored-tablet approach aquarists are familiar with from Fish Sulfa Forte.

Flexible Bottle Sizes Available in 30-count and 60-count bottles with fresh expiration dates, giving hobbyists options for short treatments, quarantine setups, or multi-tank fish rooms.

Benefits of Fix Sulfa for Fish

  • Dual-Action SMZ/TMP Combination

    Fix Sulfa pairs sulfamethoxazole and trimethoprim (SMZ/TMP), a combination aquarists use to help manage certain bacterial issues in ornamental fish when used as directed.

  • Made in the United States

    Fix Sulfa is made in the United States by Aqua Soma Labs as the current-production version of the discontinued Fish Sulfa Forte, with fresh expiration dates on every bottle.

  • Support for Common Aquarium Problems

    Aquarists commonly reach for fish sulfa tablets when dealing with symptoms associated with fin and tail rot, columnaris-type presentations, cotton wool disease, ulcer-like lesions, pop-eye, and other persistent bacterial signs in ornamental freshwater and saltwater fish.

  • Helps With External and Internal Signs of Bacterial Stress

    SMZ/TMP tablets are often used in a hospital tank for visible skin sores, fin damage, and hemorrhagic septicemia, and in situations where fish show lethargy or reduced appetite alongside water-quality corrections and supportive care.

  • Consistent 960 mg Tablet Strength

    Each tablet provides a consistent 960 mg format, making it easier to plan repeatable amounts across different tank sizes. Available in 30- or 60-tablet bottles.

  • Intended for Ornamental Fish Use

    Fix Sulfa is intended for aquarium and ornamental fish use when used as directed, and the tablet format offers a straightforward option for hobbyists who prefer predictable, countable amounts.

  • Helpful for Quarantine and Hospital Tanks

    Treating in a separate hospital or quarantine tank can help you observe fish more closely, control the amount more precisely, and reduce unnecessary exposure for healthy tank mates during treatment.

Usage Guidelines & Instructions

These steps follow the Fix Sulfa 960 bottle label directions for SMZ/TMP use in ornamental aquarium fish.

Quick Usage Summary:
Dissolve one (1) dose (one tablet) and add it for every 40 gallons (151 L) of water to be treated. Repeat every 24 hours with a partial water change between treatments for 5 to 10 days. Discontinue use if no improvement is noted after 5 days.

Before You Dose:

  • Measure Water Volume

    Calculate actual water volume (account for substrate, decor, and fill level).

  • Use a Hospital Tank

    Use a hospital/quarantine tank when possible for better control and observation.

  • Remove Carbon and UV

    Remove activated carbon and other chemical media; turn off UV sterilizers during treatment.

  • Boost Aeration

    Increase aeration and surface agitation; keep temperature stable.

Directions for Use:

  1. Dissolve and Add the Dose

    Fully dissolve one (1) dose (one tablet) in a small cup of aquarium water, then add the dissolved dose to the treatment tank. Add one tablet per 40 gallons (151 L) of water to be treated.

  2. Repeat Every 24 Hours

    Repeat every 24 hours. Perform a partial water change between treatments throughout the treatment.

  3. Complete the Treatment and Watch for Progress

    Continue treatment for 5 to 10 days. Watch appetite, swimming behavior, fin condition, and any signs of stress. Discontinue use if no improvement is noted after 5 days. If fish appear worse or show severe stress, stop treatment and seek aquatic veterinary advice.

  4. Post-Treatment Clean Up

    After the treatment is complete, perform a partial water change and resume normal filtration. Replace activated carbon or chemical media if you removed it, and keep monitoring water parameters for several days to confirm stability.

Fix Sulfa Amounts by Aquarium Size
Tank volume Fix Sulfa 960 amount How to measure
10 gallons (38 L) 1/4 tablet Split a scored tablet, or add 1/4 of one dissolved tablet
20 gallons (76 L) 1/2 tablet Split a scored tablet, or add 1/2 of one dissolved tablet
40 gallons (151 L) 1 tablet (label standard) Dissolve one whole tablet
80 gallons (303 L) 2 tablets Dissolve two whole tablets
120 gallons (454 L) 3 tablets Dissolve three whole tablets

The Fix Sulfa 960 label states one (1) dose (one tablet) per 40 gallons (151 L), which is about 24 mg of combined sulfamethoxazole and trimethoprim per gallon. The 40-gallon row is the exact label instruction; the other rows scale that same rate. For tanks under 40 gallons you can split a scored tablet, or dissolve one tablet in a measured cup of tank water and add the matching fraction for more accuracy. Dose by your treatment tank's water volume, not the number of fish, repeat once every 24 hours for 5 to 10 days, and follow the bottle label or your aquatic veterinarian over this quick-reference chart.

What to Expect During Treatment

Days 1 to 2

Fish 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.

Days 3 to 5

Watch 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 veterinarian.

Days 5 to 10

Even if the fish are improving, finish all the recommended days so the infection does not return. Afterward, run a partial water change and put activated carbon back in to clear any leftover product.

What You Need for a Treatment

A little setup before the first dose saves trouble later.

  • A separate hospital or quarantine tank, so you are not treating the whole display.
  • A heater and an air stone or sponge filter for steady temperature and strong aeration.
  • An ammonia and nitrite test kit to keep tabs on water quality.
  • A dechlorinator for the water changes between doses.
  • A small net and a clean cup for gentle transfer and measuring the dose.

Pro Tip: Hospital tank treatment helps protect the display aquarium, keeps the amount consistent, and makes it easier to keep ammonia and nitrite at 0 during recovery.

How Fix Sulfa Works

Each Fix Sulfa tablet pairs sulfamethoxazole 800 mg and trimethoprim 160 mg (SMZ/TMP). Dissolved and added to aquarium water as directed, the two ingredients work together to help slow the growth of certain bacteria.

Alongside those two ingredients, each tablet includes standard ingredients that hold the tablet together and help it disperse properly in water. Aquarists use Fix Sulfa for fin and tail rot, ulcer-like lesions, columnaris, pop-eye, and other bacterial signs in ornamental freshwater and saltwater fish.

Safety and Tank Notes

Individual fish can respond differently to treatment. For best results and safety, follow the label directions and monitor fish and water quality closely throughout the treatment.

  • Possible Side Effects in Fish

    Temporary reduced appetite, mild lethargy or hiding behavior, and occasional water cloudiness during treatment. If fish show severe distress such as rapid gill movement, gasping at the surface, loss of balance, or lying on the bottom, stop treatment, increase aeration, and seek aquatic veterinary advice.

  • Stop Treatment If

    Fish show severe stress, rapid gill movement, gasping at the surface, loss of balance, or worsening symptoms. Increase aeration immediately and consult an aquatic veterinarian if signs do not stabilize.

  • Water Quality and Biofilter Awareness

    Keep aeration strong and monitor ammonia and nitrite closely during treatment. If parameters rise, perform partial water changes as needed to keep the treatment tank stable.

  • Filtration During Treatment

    Remove activated carbon and other chemical filtration media before dosing. Turn off UV sterilizers during treatment. Resume normal filtration after the treatment is complete.

  • Invertebrates and Display Tanks

    If your system includes shrimp, snails, corals, or other invertebrates, treat fish in a separate hospital or quarantine tank whenever possible to reduce risk to the display ecosystem.

Important Warnings & Precautions

  • Aquarium Use Only

    Fix Sulfa is intended for ornamental aquarium fish only. It is not for animals raised for food.

  • Not for Food Fish

    Do not use on fish raised for food. This product is made and labeled as an antibacterial treatment for ornamental aquarium fish only.

  • Handling Note

    Avoid contact with the dissolved product, wash your hands after handling, and wear gloves if needed. Keep the tablet contents and dissolved product off skin and out of eyes.

  • Keep Out of Reach

    Store Fix Sulfa out of reach of children and pets. Use it only as directed on the product label.

  • Storage

    Keep the container tightly closed and store in a cool, dry place, away from direct sunlight and moisture. Check the expiration date and do not use tablets past it.

  • Discontinue If No Improvement

    If no improvement is noted after 5 days of treatment, discontinue use as stated on the label and re-evaluate the diagnosis or seek aquatic veterinary advice.

  • Do Not Mix Treatments

    Avoid combining Fix Sulfa with other treatments unless the product label explicitly allows it or an aquatic veterinarian advises it.

Shipping & Returns

Shipping Policy: Orders ship from our U.S. warehouse within 1 business day via USPS or UPS, with same-day dispatch on orders placed before 1:30 p.m. CT (Monday through Friday). For full shipping details, please see our shipping policy.

Refund Policy: 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 refund policy carefully.

More Fish & Bird Treatments

Fix Mox (Amoxicillin) 250/500mg A treatment for fin rot, dropsy, ulcers, and other bacterial infections in ornamental fish. Available in 30-count and 100-count capsules. Shop Fix Mox

Fix Zole (Metronidazole) 250/500mg Targets anaerobic bacteria and protozoa including Hexamita and hole-in-the-head disease in ornamental fish. Available in 60-count bottles. Shop Fix Zole

Fix Doxy (Doxycycline) 100mg A treatment for columnaris, respiratory infections, and Mycoplasma in ornamental fish and non-food pet birds. Available in 30-count and 60-count tablets. Shop Fix Doxy

Fix Zithro (Azithromycin) 250mg A treatment for fin rot, columnaris, gill disease, and avian respiratory concerns in ornamental fish and non-food pet birds. Available in 12-count and 30-count tablets. Shop Fix Zithro

Fix Cin (Clindamycin) 150mg A treatment for bacterial skin and soft tissue concerns in ornamental fish. Shop Fix Cin

Fix Pen (Penicillin) 500mg A penicillin treatment for bacterial infections in ornamental fish and non-food pet birds. Shop Fix Pen

Fix Flex (Cephalexin) 250/500mg A treatment for fin rot, ulcers, and bacterial skin infections in ornamental fish and non-food pet birds. Shop Fix Flex

Fix Flox (Ciprofloxacin) 500mg A treatment for bacterial infections including fin rot, ulcers, columnaris, and septicemia in ornamental fish and non-food pet birds. Shop Fix Flox

Browse all treatments Explore our complete Fish & Bird Antibacterials Collection for more Fix line products and related treatments.

Guides and treatment tips Visit the Fish & Bird Treatments Blog for practical usage guides, water-care advice and treatment tips.

Frequently Asked Questions

What is fish sulfa forte?

Fish Sulfa Forte was a Thomas Labs SMZ/TMP treatment (sulfamethoxazole and trimethoprim) for ornamental aquarium fish. Thomas Labs discontinued it, and Fix Sulfa by Aqua Soma Labs is the current-production version with the same two ingredients in a 960 mg tablet.

What is Fix Sulfa used for?

Fix Sulfa (SMZ/TMP) is used by aquarists to help manage certain bacterial issues in ornamental aquarium fish when used as directed. It is commonly chosen for symptoms associated with fin and tail rot, ulcer-like lesions, pop-eye, and other persistent bacterial signs.

Is Fix Sulfa the same as fish bactrim?

Yes, in the sense that Bactrim is another name for the same sulfamethoxazole and trimethoprim combination. Hobbyists searching for fish bactrim or bactrim for fish are looking for an SMZ/TMP tablet, and Fix Sulfa supplies sulfamethoxazole 800 mg with trimethoprim 160 mg per 960 mg tablet. The two ingredients work together against certain bacteria, which is why the pairing is described as dual-action.

What is the difference between Fish Sulfa Forte, Aqua Sulfa and Fix Sulfa?

Fish Sulfa Forte (Thomas Labs), FISHBIOTIC SMZ/TMP and Aqua Sulfa are older names for the same sulfamethoxazole and trimethoprim tablet. Thomas Labs discontinued Fish Sulfa Forte, and Fix Sulfa by Aqua Soma Labs is the current-production version, with sulfamethoxazole 800 mg and trimethoprim 160 mg in the same 960 mg tablet format. The brand name and maker changed; the tablet and its intended use did not.

What is inside each Fix Sulfa tablet?

Each scored tablet contains sulfamethoxazole 800 mg and trimethoprim 160 mg, which is where the 960 mg figure comes from. The rest of the tablet is standard ingredients that hold it together and help it disperse in water. Fix Sulfa is made and labeled only for ornamental aquarium fish, not for animals raised for food.

What is the fish sulfa dosage per gallon?

The Fix Sulfa 960 label directs one (1) dose (one tablet) per 40 gallons (151 L) of water to be treated, about 24 mg of combined sulfamethoxazole and trimethoprim per gallon. Repeat every 24 hours with a partial water change between treatments for 5 to 10 days, and discontinue use if no improvement is noted after 5 days. Because one tablet covers 40 gallons, smaller tanks need a fraction: split a scored tablet, or dissolve one tablet in a measured cup of tank water and add the matching share. Dose by the water volume of your treatment tank, not by the number of fish.

Is Fix Sulfa the same as Triple Sulfa for fish?

No. Triple Sulfa aquarium products combine three different sulfa compounds and are usually sold as a powder for the whole tank. Fix Sulfa is a two-ingredient tablet: sulfamethoxazole paired with trimethoprim, which is the SMZ/TMP combination. They are not interchangeable, so follow the directions for the specific product you actually have.

Can Fix Sulfa be used for dogs or cats?

Fix Sulfa is labeled for ornamental aquarium fish only. Veterinarians do use sulfamethoxazole and trimethoprim in dogs and cats, but the correct amount depends on the animal's weight and the format differs from an aquarium tablet. Do not give Fix Sulfa to a dog, cat or horse without a licensed veterinarian confirming the diagnosis and the amount. It is also not for animals raised for food.

Where can I buy SMZ/TMP fish tablets? Do Walmart or Tractor Supply sell them?

You can order Fix Sulfa, the current SMZ/TMP fish tablet, directly from Fine Pet Health in 30-count and 60-count bottles of 960 mg tablets. General retailers such as Walmart, Tractor Supply, PetSmart and Petco do not carry the Aqua Soma Labs line, so a dedicated online supplier is the reliable route. Orders ship from our U.S. warehouse via USPS or UPS, with same-day dispatch on orders placed before 1:30 p.m. CT, Monday through Friday.

Browse Fish & Bird Treatments Collection →
Can Fix Sulfa treat fungal, viral, or parasitic infections?

Fix Sulfa (SMZ/TMP) is an antibacterial treatment intended for certain bacterial issues. It is not designed for fungal, viral, or parasitic problems. If you suspect fungus, parasites, or mixed causes, consult an aquatic veterinarian or experienced aquarist to choose an appropriate treatment plan.

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Who is responsible for this page: the Fine PetHealth Editorial Team, part of Fine PetHealth Group LLC, a US-based pet supplies retailer.

How this page was created: prepared with AI assistance, verified against the current product label, and reviewed by a person before publishing. How we verify product information.

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