What Is Fish Mox? Amoxicillin for Aquarium Fish Explained
What Fish Mox is
"Fish Mox" is a familiar name in the aquarium hobby for capsules that contain amoxicillin, a widely used antibiotic. The capsules are labeled for ornamental aquarium fish, and the name comes from "amoxicillin". PetRemedyUSA sells them as Fish Mox 250mg and Fish Mox 500mg.
How amoxicillin works
Amoxicillin is a beta-lactam antibiotic. It stops bacteria from building their cell walls, which kills susceptible bacteria as they grow. It is most effective against gram-positive bacteria and some gram-negative bacteria.
What keepers commonly use it for
- Fin rot and tail rot, see our fin rot guide
- Bacterial ulcers, wounds and skin infections
- Secondary bacterial infections after injury or handling
What Fish Mox will not treat
Antibiotics act only on bacteria. Fish Mox will not cure external parasites such as ich or velvet, internal protozoa, or true fungal infections. If a fish has white dots, fluffy growth or another non-bacterial problem, a different treatment is needed. Our antibiotic comparison and columnaris versus fungus guide help you tell them apart.
Strengths and pack sizes
| Product | Amoxicillin per capsule | Typical use |
|---|---|---|
| Fish Mox 250mg | 250 mg | Smaller tanks and general use |
| Fish Mox 500mg | 500 mg | Larger systems, fewer capsules to handle |
The active ingredient is identical. The only difference is how much amoxicillin each capsule holds. See Fish Mox vs Fish Mox Forte for how the names relate.
Using it responsibly
- Follow the directions on the label of the product you receive, and complete the full course.
- Treat in a hospital tank so your main filter is not disturbed.
- Remove activated carbon while medicating, since it absorbs medication.
- Test water daily, see water quality during treatment.
- People with a penicillin allergy should avoid handling the capsules and treated water without gloves.
Is it the same as human amoxicillin?
The active ingredient is the same compound, but Fish Mox is labeled and sold for ornamental aquarium fish only. It is not for human use and not for fish intended for food. Rules for animal medications vary, so consult a veterinarian if you are unsure whether it suits your animals.
Frequently asked questions
What is Fish Mox used for?
It is commonly used by aquarium keepers for bacterial problems such as fin rot, ulcers and skin infections. It only works on bacteria.
What is the active ingredient in Fish Mox?
Amoxicillin, a penicillin-class antibiotic. The capsules are available in 250mg and 500mg strengths.
Does Fish Mox treat ich?
No. Ich is a parasite and antibiotics do not act on parasites. It needs a parasite-specific treatment.
Can I use Fish Mox with other medications?
Combining medications can stress fish and change how each drug works. Unless a veterinarian or the label directs it, use one treatment at a time.
Is Fish Mox safe for people?
It is not for human use. People with penicillin allergies should wear gloves when handling it. Keep it out of reach of children.