Fish Azithromycin 250mg for Fin Rot, Columnaris and Gill Disease in
Freshwater and Saltwater Tanks
Fish Zithro (Bird Zithro) supplies 250mg azithromycin per tablet and is an antibacterial treatment for ornamental aquarium fish and non-food pet birds. It is often chosen to help manage suspected bacterial problems such as fin and tail rot, columnaris, gill disease and early respiratory signs in pet birds. The standard fish amount is one 250 mg tablet per 10 gallons (38 L) of water, repeated every 24 hours for 5 to 7 days.
Often called Bird Zithro or Fish Zithro in the hobby community, Fix Zithro is a reliable replacement for the discontinued Thomas Labs Bird Zithro, Fish Zithro and Aqua Zithro 250 mg products. Some keepers also search for it as fish zithromax or a fish z pack, since Zithromax and Z-Pak are other names for azithromycin.
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.
Important Notice: This product is intended for aquarium and ornamental fish and pet birds only. It is not for animals used for food. Not for human use.
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This azithromycin tablet from the Aqua Soma Labs Fix range is used for 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, for mild upper respiratory tract infections (URI), suspected Mycoplasma issues, or conditions like chlamydia psittaci (psittacosis / parrot fever) in pigeons and other pet birds.
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.
Fix Zithro from Aqua Soma Labs 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 flock treatment and loft management for a busy aviary.
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.
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 Azithromycin, Same Strength Fix Zithro contains the same 250 mg azithromycin per tablet that you relied on with Bird Zithro and Aqua Zithro. The same formula 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
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Bacterial Support for Fish & Birds
Fix Zithro provides 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.
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Ready to Use Promptly
Keep Fix Zithro on hand so you can begin treatment as soon as you notice early signs of bacterial stress. For pet birds, professional veterinary guidance is still strongly recommended to set the correct amount and duration.
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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.
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Consistent 250 mg Tablets
Each tablet delivers a consistent 250 mg of azithromycin, making it easier to scale treatment from a single betta or quarantine tank up to larger community aquariums, lofts or aviaries without complicated calculations.
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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.
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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.
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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.
Usage Guidelines & Instructions
Directions for Use:
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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.
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Directions 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 to 7 days while closely monitoring water quality and fish behavior. This is the standard amount for fish unless your aquatic veterinarian advises otherwise.
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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 amount for the bird's weight, frequency and duration. Tablets may be given whole, split, or crushed and mixed into soft food or drinking water exactly as instructed.
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Maintain Water Quality & Finish the Treatment
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 number of days 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.
| Tank volume | Azithromycin per use | 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.
Amounts for Pet Birds
Birds are given an amount based on body weight, 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 amount, 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 amounts 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 treatment so the infection does not return. Afterward, run a partial water change and put activated carbon back in to clear any leftover azithromycin from the water.
What You Need for Treatment
A bit of 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 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 Fix Zithro Works
Azithromycin works to help slow or stop the growth of certain bacteria in the gills, skin and respiratory tract. Used as directed in fish or birds, it works best alongside good husbandry, clean water and appropriate nutrition.
The rest of each tablet is made up of standard ingredients that hold the tablet together, keep the azithromycin stable on the shelf, and let the tablet disperse and dissolve when added to aquarium water or mixed with soft food.
Safety and Tank Notes
When used as directed, Fix Zithro usually causes no problems in ornamental fish and non-food pet birds. As with any azithromycin product, incorrect amounts or prolonged use can increase the risk of side effects and resistance.
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Fish
Azithromycin-based fish treatments 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.
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Birds
When azithromycin is given in food or drinking water, possible reactions include decreased appetite, loose or changed droppings and lethargy, especially if the amount 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.
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Invertebrates
Do not use Fix Zithro in display tanks that contain shrimp, snails or other invertebrates, as strong antibacterial treatments may harm them or disrupt the tank ecosystem. Whenever possible, move affected fish to a separate hospital tank.
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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 antibacterial treatments unless advised by a veterinarian.
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Important safety warning
Fix Zithro is intended for ornamental aquarium fish and non-food pet birds only, and not for animals raised for food. 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.
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Frequently Asked Questions
What is Fix Zithro (Bird Zithro) used for in fish and birds?
Fix Zithro (azithromycin 250 mg) is an antibacterial treatment 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.
What does azithromycin treat in fish?
In aquarium fish, azithromycin is mainly used for bacterial problems such as fin and tail rot, columnaris, gill disease, and ulcers, in both freshwater and saltwater tanks. It works against certain bacteria affecting the gills, skin and respiratory tract. For non-food pet birds, azithromycin is used under avian veterinary guidance for respiratory and Mycoplasma-related concerns.
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 the same as Fish Zithro or Aqua Zithro?
Yes. Fish Zithro and Aqua Zithro were earlier names for azithromycin 250 mg products in the hobby, alongside Thomas Labs Bird Zithro. Fix Zithro from Aqua Soma Labs is the current direct replacement, with the same 250 mg azithromycin per tablet and the same 12-count and 30-count bottle sizes. Product names and packaging have changed, but the tablet and its intended fish and bird use remain the same.
Is azithromycin for birds the same as fish azithromycin?
Same azithromycin. Fix Zithro gives you 250 mg azithromycin per tablet for both ornamental fish and non-food pet birds. What changes is the amount: fish go by tank volume, birds go by body weight, and a bird should only be treated when an avian vet has set the amount.
What is the fish azithromycin dosage?
The standard fish azithromycin dosage is one 250 mg tablet per 10 gallons (38 L) of tank water, about 25 mg per gallon, dosed every 24 hours for 5 to 7 days with partial water changes between doses. For tanks under 10 gallons, split a tablet to match the actual water volume. Birds are different: an avian veterinarian sets the amount by body weight, so do not estimate bird amounts from the aquarium chart.
Is fish azithromycin available in 500 mg?
Fix Zithro comes as 250 mg tablets only. If you need 500 mg total, 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 schedule on the label.
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 amount and schedule before treating pigeons. Fix Zithro is also not for chickens, ducks, or other food-producing birds.
Where can I buy azithromycin for fish? Do Walmart or PetSmart sell it?
You can order Fix Zithro, the current fish and bird azithromycin, directly from Fine Pet Health in 12-count and 30-count bottles of 250 mg tablets. General retailers such as Walmart, PetSmart, Petco, and Tractor Supply 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 Zithro treat fungal, viral or parasitic infections?
No. Fix Zithro is an azithromycin antibacterial treatment for fish and birds 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.