Fix Zithro (Fish Zithro) Azithromycin 250mg is a pharmaceutical-grade, broad-spectrum fish and bird antibiotic for ornamental aquarium fish and non-food pet birds. Often called Bird Zithro or Fish Zithro in the hobby community, Fix Zithro is a reliable online alternative to discontinued Thomas Labs Bird Zithro, Fish Zithro and Aqua Zithro 250 mg products.
This over-the-counter (OTC) azithromycin tablet from the Aqua Soma Labs Fix range helps manage common problems such as fin and tail rot, columnaris, gill disease, bacterial hemorrhagic septicemia, and other bacterial infections in freshwater and saltwater aquariums. Bird keepers also use it, under veterinary guidance, as a bird azithromycin option for mild upper respiratory tract infections (URI), suspected Mycoplasma issues, or conditions like chlamydia psittaci (psittacosis / parrot fever) in pigeons and other pet birds.
Azithromycin is a macrolide antibiotic that works by interfering with bacterial protein synthesis, which helps slow or stop the growth of susceptible bacteria in the gills, skin and respiratory tract. When used as directed in fish or birds, azithromycin can be part of a broader management plan that also includes good husbandry, clean water and appropriate nutrition.
Fix Zithro from Aqua Soma Labs supplies 250 mg azithromycin per tablet and is available to buy online in bottles of 12 or 30 tablets with fresh expiration dates. This gives hobbyists flexible options, whether they maintain a single hospital tank, multiple community aquariums, or need effective flock treatment and loft management for a busy aviary.
Use Fix Zithro when you notice early signs of bacterial stress. The warning signs differ between fish and birds, so the lists below split them by species.
Fish-Specific Symptoms
Clamped or frayed fins (fin and tail rot)
Red or cloudy patches on the body
Fuzzy patches that suggest columnaris
Pop-eye (exophthalmia)
Gill irritation or labored gill movement
Secondary infections around gill flukes
Listlessness or a persistent loss of appetite
Bird-Specific Symptoms
Sneezing and nasal discharge
Upper respiratory tract infections (URI)
Swollen eyes or sinus infections
Suspected Mycoplasma issues
Signs linked to chlamydia psittaci (parrot fever)
Ruffled feathers, fluffed-up posture
Reduced activity or loss of appetite
Treat bacterial issues early, keep the water clean, and ask an aquatic or avian professional when one is available. That combination gives your fish and birds the best chance to recover and keeps the aquarium or aviary stable.
Order online for same-day dispatch on orders placed before 1:30 p.m. CT, Monday through Friday. Fix Zithro ships directly from our U.S. warehouse via USPS or UPS.
Important Notice: This product is intended for aquarium and ornamental fish and pet birds only. It is not for human consumption or for animals used for food. We do not sell or recommend this product for human use.
Bird Zithro vs Fix Zithro: What Changed?
If you previously purchased Thomas Labs Bird Zithro, Fish Zithro or Aqua Zithro, here is what has changed and what remains the same:
Same Active Ingredient Fix Zithro contains the same 250 mg azithromycin per tablet that you relied on with Bird Zithro and Aqua Zithro. The pharmaceutical-grade formulation targets the same bacteria.
New Manufacturer Fix Zithro is made by Aqua Soma Labs, replacing the discontinued Thomas Labs line. Aqua Soma Labs manufactures in the United States under strict quality-control standards.
Same Tablet Form Fix Zithro uses the same crushable tablet format as the original Bird Zithro, making it easy to dissolve in aquarium water or mix with soft food for birds.
Available in 12-Count and 30-Count Bottles Choose the size that fits your setup: a 12-count bottle for a single hospital tank or occasional use, or a 30-count bottle for larger collections, multi-tank operations or aviary flock management.
Benefits of Fix Zithro for Fish & Birds
Broad-Spectrum Bacterial Support
Fix Zithro provides broad-spectrum azithromycin coverage for ornamental fish and non-food pet birds. It helps manage common problems such as fin and tail rot, columnaris, gill disease, and early respiratory signs or the ornithosis complex in birds when used as directed.
No Veterinary Prescription Required
Fix Zithro is available over the counter for aquarium and avian use, so you can start treatment promptly without waiting for a prescription. For birds, professional veterinary guidance is still strongly recommended to determine the correct dose and duration.
Helps With Internal and External Infections
Azithromycin in Fix Zithro can be used for skin lesions, ulcers, fin damage and internal infections in a hospital tank, as well as part of a treatment plan for mild respiratory or Mycoplasma-related concerns in pet birds.
Consistent 250 mg Tablets
Each tablet delivers a reliable 250 mg azithromycin dose, making it easier to scale treatment from a single betta or quarantine tank up to larger community aquariums, lofts or aviaries without complicated calculations.
Easy to Administer
These crushable tablets are easy to mix and can be dissolved directly in aquarium water or mixed with soft food, providing flexible options for shy, stressed or hard-to-handle fish and birds while minimizing handling and extra stress.
Versatile for Freshwater, Saltwater & Aviary Setups
Hobbyists reach for Fix Zithro as their trusted choice in both freshwater and marine systems, and as a convenient option for pigeons and other ornamental birds kept in lofts, cages or aviaries.
Ideal for Hospital Tanks and Quarantine
Using Fix Zithro in a separate hospital tank or treatment cage helps protect the main aquarium's biofilter and reduces unnecessary exposure of healthy tank mates or flock members while you focus treatment where it is needed most.
Dosage Guidelines & Instructions
Directions for Use:
Set Up a Separate Treatment Area
Move affected fish to a dedicated hospital tank and, where practical, house birds needing treatment in a small treatment cage. This helps protect healthy tank mates or flock members and lets you control dosing more precisely.
Dose for Fish Aquariums
Dissolve one 250 mg tablet per 10 gallons (38 L) of water in the hospital tank. Mix the tablet in a small cup of aquarium water first, then distribute it evenly around the tank. Repeat the dose every 24 hours for 5-7 days while closely monitoring water quality and fish behavior. This is the standard dosage for fish unless your aquatic veterinarian advises otherwise.
Use in Pet Birds (Under Veterinary Guidance)
Only administer Fix Zithro to pigeons and other pet birds under the direction of an avian veterinarian. Your vet can advise you on the correct mg-per-kg dose, frequency and duration. Tablets may be given whole, split, or crushed and mixed into soft food or drinking water exactly as instructed.
Maintain Water Quality & Complete the Course
Perform partial water changes as needed between doses to keep ammonia and nitrite low and ensure good aeration in the hospital tank. Continue treatment for the full recommended course even if fish or birds appear better; stopping early can allow symptoms to return. If there is no improvement after several days, or if signs worsen, consult an aquatic or avian professional.
Fix Zithro Dosing by Aquarium Size
Tank volume
Azithromycin per dose
250 mg tablets
10 gallons (38 L)
250 mg
1
20 gallons (76 L)
500 mg
2
30 gallons (114 L)
750 mg
3
40 gallons (151 L)
1000 mg
4
55 gallons (208 L)
about 1375 mg
5 to 6
These numbers follow the label guideline of one 250 mg tablet per 10 gallons, about 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 7 days, and round to the nearest practical tablet. Split a tablet for tanks under 10 gallons. The bottle label or your aquatic veterinarian takes priority over this quick-reference chart.
Dosing for Pet Birds
Birds are dosed by body weight (mg per kg), not by water volume, so there is no single chart the way there is for aquariums. The right amount depends on the species, the bird's weight and the specific infection. An avian veterinarian sets the mg-per-kg dose, how often to give it, and how long to continue. Crush and mix the tablet into soft food or drinking water exactly as your vet directs, and do not estimate avian doses on your own.
What to Expect During Treatment
Days 1 to 2
Fish may hide or eat less, and the water can look slightly cloudy. That is normal at the start. Keep dosing on schedule and keep aeration strong.
Days 3 to 5
Watch for signs it is working: fin damage and red patches stop spreading, appetite returns, and breathing steadies. If nothing changes by day 5, or the fish look worse, stop and ask an aquatic veterinarian.
Days 5 to 7
Even once the fish improve, finish the full course so the infection does not return. Afterward, run a partial water change and put activated carbon back in to clear any leftover medication.
What You Need for a Treatment Course
A bit of setup before the first dose saves trouble later.
A separate hospital or quarantine tank, so you are not medicating 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 for mixing the dose.
Pro Tip: Always quarantine infected fish and birds away from healthy companions during treatment to reduce stress and help prevent the spread of disease. A small, dedicated hospital tank with a heater, air stone and no substrate makes dosing and water changes easier.
How This Medication Works
Active ingredient: Azithromycin (250 mg per tablet)
Azithromycin is a macrolide antibiotic that interferes with bacterial protein synthesis, helping slow or stop the growth of susceptible bacteria in the gills, skin and respiratory tract of ornamental fish and non-food pet birds.
Inactive ingredients
Tablet excipients that help keep the azithromycin stable on the shelf and allow the tablet to disperse and dissolve properly when added to aquarium water or mixed with soft food.
Side Effects & Safety Tips
When used as directed, Fix Zithro is generally well tolerated in ornamental fish and non-food pet birds. As with any azithromycin product, incorrect dosing or prolonged use can increase the risk of side effects and antibiotic resistance.
Fish
Azithromycin-based fish antibiotics may cause temporary stress or hiding behavior, mild water cloudiness and reduced appetite during treatment. If fish show severe distress such as rapid gill movement, loss of balance, gasping at the surface or lying on the bottom, stop treatment, improve aeration and seek aquatic veterinary advice.
Birds
When azithromycin is given in food or drinking water, possible reactions include decreased appetite, loose or changed droppings and lethargy, especially if the dose is too high or the bird is sensitive. If your bird appears fluffed up, inactive or stops eating, discontinue use and contact an avian veterinarian.
Invertebrates
Do not use Fix Zithro in display tanks that contain shrimp, snails or other invertebrates, as strong antibiotics may harm them or disrupt the tank ecosystem. Whenever possible, move affected fish to a separate hospital tank.
Safe use in your system
Treat fish in a hospital or quarantine tank whenever you can, remove activated carbon and turn off UV sterilizers during treatment, and monitor ammonia, nitrite and temperature closely. Do not mix Fix Zithro with other antibiotics unless advised by a veterinarian.
Important safety warning
Fix Zithro is intended for ornamental aquarium fish and non-food pet birds only. It is not for human use and not for animals raised for food. Using fish or bird antibiotics in people instead of prescribed medicine can lead to treatment failure, serious side effects and antibiotic resistance. Store tablets in a cool, dry place away from direct sunlight and keep out of reach of children and pets. Always follow the directions on the label.
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.
Frequently Asked Questions
What is Fix Zithro (Bird Zithro) used for in fish and birds?
Fix Zithro (azithromycin 250 mg) is a fish and bird antibiotic used by hobbyists to help manage bacterial issues such as fin and tail rot, columnaris or gill disease in ornamental aquarium fish, and to support veterinarian-directed treatment of mild respiratory or Mycoplasma-related problems in non-food pet birds.
Is fish azithromycin the same as human azithromycin?
Both contain azithromycin, but Fix Zithro is made and labeled for ornamental fish and non-food pet birds, not for people. Human medicine should come from a licensed pharmacy with a doctor's guidance. Never use fish azithromycin for people or for animals raised for food.
What is the difference between Bird Zithro and Fix Zithro?
Bird Zithro was the brand name used by Thomas Labs for their azithromycin 250 mg tablets. After Thomas Labs discontinued the product, Aqua Soma Labs introduced Fix Zithro as a direct replacement. Fix Zithro contains the same 250 mg azithromycin per tablet, uses the same crushable tablet format, and is intended for the same ornamental fish and pet bird applications.
Is Fix Zithro a replacement for Aqua Zithro?
Yes. If you previously used Aqua Zithro 250 mg, Fix Zithro from Aqua Soma Labs is a direct replacement with the same active ingredient (azithromycin 250 mg per tablet) and is available in the same 12-count and 30-count bottle sizes.
Is Fix Zithro the same as Fish Zithro?
Fish Zithro was another name used for azithromycin fish antibiotic products. Fix Zithro from Aqua Soma Labs contains the same 250 mg azithromycin active ingredient and is a modern replacement for older Fish Zithro products that are no longer manufactured.
Can I buy fish azithromycin without a vet prescription?
Yes. Fix Zithro is sold over the counter as a fish azithromycin antibiotic, so no veterinary prescription is needed to buy it for ornamental fish. For pet birds, ask an avian vet to set the correct mg-per-kg dose and how long to treat.
Do I need a veterinary prescription to buy Fix Zithro?
No. Fix Zithro is sold over the counter as a fish and bird antibiotic, and no veterinary prescription is required to purchase it. However, for pet birds, professional veterinary guidance is strongly recommended to determine the correct mg-per-kg dose and treatment duration.
Where can I buy azithromycin for fish online?
You can buy Fix Zithro (azithromycin 250 mg) directly from Fine Pet Health. Orders ship from our U.S. warehouse with same-day dispatch on orders placed before 1:30 p.m. CT, Monday through Friday, via USPS or UPS.
Is azithromycin stronger than amoxicillin for fish?
Neither one is just stronger. They are different classes of antibiotic that hit different bacteria. Azithromycin is a macrolide (in Fix Zithro); amoxicillin is a penicillin-type drug (in Fix Mox). Which one works depends on what is making the fish sick, so it helps to confirm the likely bacteria with an aquatic vet or an experienced aquarist before you choose.
How do I know if my fish might need a fish azithromycin antibiotic?
Watch for signs such as frayed or rotting fins, red or white ulcers, fuzzy patches that suggest columnaris, labored breathing or listless behavior that does not improve with good water quality and husbandry. A fish veterinarian or experienced aquarist can help confirm whether a bacterial infection is likely and whether azithromycin treatment is appropriate.
Is azithromycin for birds the same as fish azithromycin?
Same active ingredient. Fix Zithro gives you 250 mg azithromycin per tablet for both ornamental fish and non-food pet birds. What changes is how you dose it: fish go by tank volume, birds go by body weight (mg per kg), and a bird should only be treated when an avian vet has set the dose.
What size aquarium can one Fix Zithro tablet treat?
One 250 mg tablet treats approximately 10 gallons (38 liters) of aquarium water. For a 20-gallon hospital tank, you would use two tablets per dose. Always dose based on the actual water volume in the treatment tank, not the manufacturer-listed tank size, since gravel, decorations and equipment reduce usable volume.
Is fish azithromycin available in 500 mg?
Fix Zithro comes as 250 mg tablets only. If you need a 500 mg total dose, use two 250 mg tablets per the label directions or your veterinarian's guidance. Measure the tank volume or the bird's body weight first, and do not go past the dosing schedule on the label.
Can I use Fix Zithro in my main community or reef tank?
It is best to treat sick fish in a separate hospital tank instead of the main aquarium. Fix Zithro and other fish azithromycin products are not recommended for reef tanks or setups with shrimp, snails, corals or other invertebrates, because strong antibiotics may harm them or disrupt beneficial filter bacteria.
Does Fix Zithro work in saltwater aquariums?
Yes. Fix Zithro can be used in both freshwater and saltwater hospital tanks. Dissolve the tablet following the standard dosage (one 250 mg tablet per 10 gallons) and maintain stable salinity, temperature and water quality parameters throughout the treatment course.
How long should I treat with Fix Zithro?
For fish, many hobbyists follow the label directions of one 250 mg tablet per 10 gallons (38 L) once every 24 hours for 5-7 days, or as advised by an aquatic veterinarian. Birds should only receive Fix Zithro for the dose and duration prescribed by an avian vet, who will decide how long treatment should continue.
Can Fix Zithro be used for racing pigeons?
Pigeon keepers use azithromycin under veterinary guidance for respiratory and Mycoplasma-related concerns in racing and show pigeons. Fix Zithro provides the same 250 mg azithromycin per tablet found in older Bird Zithro products that were widely used in loft management. Always consult an avian vet for the correct dosage and treatment schedule before administering to pigeons.
Can I combine Fix Zithro with other fish medications?
Combining antibiotics or mixing Fix Zithro with antifungal or antiparasitic medications is generally not recommended unless specifically advised by an aquatic veterinarian. Using multiple medications at once can stress fish, cause unpredictable interactions and make it harder to identify which treatment is working.
Can Fix Zithro treat fungal, viral or parasitic infections?
No. Fix Zithro is an azithromycin fish and bird antibiotic that targets certain bacterial infections only. It is not effective 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 an appropriate treatment instead of using an antibiotic.
Is Fix Zithro safe for betta fish and small aquariums?
Yes. Fix Zithro can be used in small hospital tanks for bettas and other individual fish. Because bettas are often kept in tanks under 10 gallons, you may need to split a tablet to achieve the correct dose (one 250 mg tablet per 10 gallons). Dissolve the portion in a small cup of tank water before adding it to the hospital tank.
How should I store and dispose of Fix Zithro tablets?
Store tablets in their original container in a cool, dry place away from heat, moisture, children and pets. Follow local guidelines for pharmaceutical disposal and avoid flushing unused tablets down the drain unless specifically instructed by local authorities.
More Fish & Bird Antibiotics
Fix Mox (Amoxicillin) 250/500mg A broad-spectrum penicillin-type fish antibiotic for fin rot, dropsy, ulcers and other bacterial infections. 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 tetracycline-class fish and bird antibiotic effective against columnaris, respiratory infections and Mycoplasma. Available in 30-count and 60-count tablets. Shop Fix Doxy
Fix Cin (Clindamycin) 150mg A lincosamide fish antibiotic commonly used for gram-positive bacterial infections including skin and soft tissue concerns in ornamental fish. Shop Fix Cin
Fix Sulfa (SMZ/TMP) 960mg A sulfonamide combination fish antibiotic offering broad-spectrum coverage against a range of bacterial infections in ornamental fish. Shop Fix Sulfa
Fix Pen (Penicillin) 500mg A penicillin-type fish and bird antibiotic for gram-positive bacterial infections in ornamental fish and non-food pet birds. Shop Fix Pen
Fix Flex (Cephalexin) 250/500mg A first-generation cephalosporin fish and bird antibiotic for fin rot, ulcers and bacterial skin infections in ornamental fish. Shop Fix Flex
Fix Flox (Ciprofloxacin) 500mg A fluoroquinolone fish and bird antibiotic for gram-negative bacterial infections including fin rot, ulcers, columnaris and septicemia in ornamental fish. Shop Fix Flox
Guides and treatment tips Visit the Fish & Bird Antibiotics Blog for practical dosing guides, water-care advice and treatment tips.
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About Fine PetHealth and How We Verify Our Antibiotic Guides
Who is responsible for this page: Fine PetHealth Editorial Team.
Verification snapshot: This guide is written from the current product label for this item and reviewed for accuracy and consistency before publishing.
How we verify product information (our checklist):
1) Label-first accuracy: Dosing, duration, storage, and warnings are taken from the current product label for this item.
2) Ingredient validation: Active ingredient names are cross-checked against reputable references (for example, NIH PubChem) to reduce the risk of labeling mistakes.
3) Consistency checks: We review for internal consistency (the same dosing and storage language across sections) and remove wording that could overpromise results.
4) Updates: We update pages when label directions, packaging, or manufacturer information changes.
What we don’t do: We don’t invent diagnoses, and we don’t create dosing instructions beyond what the product label states for this item’s intended use.
See something that doesn’t match your bottle? Please contact us so we can review and update the page:
Contact Fine PetHealth.
Educational use: Our content is for informational purposes and is not a substitute for diagnosis or treatment from an aquatic or avian veterinarian.
Hi Leaf, we really appreciate the awesome review! It’s great to hear the Fix Zithro hit the mark and was a perfect fit for your tank. Let us know whenever you need to restock!
K
Kathy Carlson (Washington, IA)
Fast shipping
My fish needed treatment and they delivered quickly. Thanks!
Hi Kathy, thank you for the great review! We know how stressful it is when your fish need treatment, so we're thrilled the Fix Zithro arrived right on time. Wishing them a speedy recovery!
A
Andres Navarro (Citrus Heights, CA)
Good product
Fast shipping good seller
Hi Andres! We really appreciate you taking a quick moment to leave such a wonderful five-star rating. We are completely thrilled that you were pleased with the rapid delivery and the excellent quality of the Fix Zithro. Your kind feedback means the world to our team, and we would be absolutely honored to assist you again the next time you need to stock up!
R
Richard M Buss (St Louis, MO)
Campground has legionella/streptococcus bacteria in water
Azithromycin helps this bacteria. And I use RO water 100%
Hey Richard, thanks so much for the 5-star rating! Dealing with water issues at a campground sounds pretty stressful, so we're really glad the Fix Zithro is coming in handy for your situation. Stay safe out there, and thanks for choosing us!
Hi Jason, just wanted to say a quick thank you for the perfect score on your Fix Zithro order. We're super grateful for your business and are always here if you need anything else!
