Fix Sulfa (Fish Sulfa Forte) Tablets - 960 mg

Fix Sulfa (Fish Sulfa) SMZ/TMP 960 mg is an over-the-counter (OTC) fish antibiotic for ornamental aquarium fish. This sulfamethoxazole and trimethoprim combination (SMZ/TMP) from Aqua Soma Labs is a current-production, dual-ingredient antibiotic that aquarists use to help manage suspected bacterial infections in freshwater and saltwater aquariums.

In older hobby listings and aquarium forums, this SMZ/TMP medication also goes by Fish Sulfa, Fish Sulfa Forte, FISHBIOTIC SMZ/TMP, Aqua Sulfa, and informally "fish Bactrim" or "Bactrim for fish," because Bactrim is a human brand of the same two ingredients. 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 caused by susceptible gram-negative and gram-positive bacteria such as Aeromonas, Vibrio, or Streptococcus.

SMZ/TMP (co-trimoxazole) is a dual-ingredient antibiotic that works on bacterial folate synthesis at two steps, which helps slow or stop the growth of susceptible bacteria. When used as directed for fish, sulfamethoxazole/trimethoprim works best alongside stable water parameters, strong aeration, and good husbandry. Fix Sulfa is the current-production version, and it does not require a prescription.

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.

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.

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.

Important Notice: This product is intended for aquarium and ornamental fish only. It is not for human consumption or for animals used for food. We do not sell or recommend this product for human use.

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:

Benefits of Fix Sulfa for Fish

• Dual-Action SMZ/TMP Combination

  Fix Sulfa combines sulfamethoxazole and trimethoprim (SMZ/TMP), a paired approach that interferes with bacterial folate production at two steps to help manage susceptible bacterial issues when used as directed.

• No Prescription Required

  Fix Sulfa is available over the counter (OTC) for aquarium and ornamental fish. You can order online and have it shipped directly without needing a veterinary prescription.

• Broad-Spectrum 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 dosing 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 dosing.

• Helpful for Quarantine and Hospital Tanks

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

Dosage Guidelines & Instructions

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

Dosage Quick Reference:
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 5-10 days. Discontinue use if no improvement is noted after 5 days.

Before You Dose:

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

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

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

• 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. Dose at one tablet per 40 gallons (151 L) of water to be treated.

2. Repeat Every 24 Hours

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

3. Complete the Course and Watch for Progress

   Continue treatment for 5-10 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 course 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.

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

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

How It Works

• Active Ingredients (each tablet)

  Sulfamethoxazole 800 mg and Trimethoprim 160 mg (SMZ/TMP, also known as co-trimoxazole). This paired combination works at two steps in bacterial folate synthesis, which helps slow the growth of susceptible bacteria when used as directed. The chemical identity and properties of these active ingredients are documented by NIH PubChem: sulfamethoxazole, CID 5329 and trimethoprim, CID 5578.

• Inactive Ingredients

  Tablet excipients that help keep the active ingredients stable and allow the tablet to disperse properly when dissolved and added to aquarium water as directed. Inactive ingredients are not specified in the active-ingredient panel.

Shipping & Returns

Frequently Asked Questions

Bottom Line

Sources

Key references used to check the drug facts on this page. Always follow the directions on your product's label.

• NIH PubChem. Sulfamethoxazole, Compound CID 5329 (chemical identity and properties). pubchem.ncbi.nlm.nih.gov
• NIH PubChem. Trimethoprim, Compound CID 5578 (chemical identity and properties). pubchem.ncbi.nlm.nih.gov
• University of Florida IFAS Extension. Yanong, R.P.E. Use of Antibiotics in Ornamental Fish Aquaculture (FA084). edis.ifas.ufl.edu

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