Fish Mox vs Fish Mox Forte: Which Strength Does Your Tank Need?

Fish Mox and Fish Mox Forte are the same medication — amoxicillin for ornamental fish — at two strengths: 250 mg and 500 mg per capsule. The right choice comes down to tank volume: the 250 mg strength is the standard pick for most home aquariums, while the 500 mg forte strength saves capsules on large tanks and multi-tank systems.

Side-by-side comparison

	Fish Mox 250 mg	Fish Mox Forte 500 mg
Amoxicillin per capsule	250 mg	500 mg
Capsules per bottle	100	100
Typical fit	Tanks up to ~55 gallons	Large tanks, ponds’ quarantine systems, fish rooms
Capsules per treatment day*	More on big tanks	Half as many for the same total dose
Also searched as	fishmox, fish-mox	fish mox forte, fishmox forte

*Always follow the directions printed on your bottle — strengths and directions vary by label.

When the 250 mg strength makes sense

If you keep a single community tank, a betta setup, or anything up to roughly a 55-gallon aquarium, the 250 mg strength is the straightforward choice. Dosing granularity is actually an advantage in smaller volumes of water — it’s easier to match the label’s per-gallon directions without splitting capsules.

When to step up to Forte 500 mg

Keepers dosing 75–125+ gallon tanks, multiple quarantine systems, or a whole fish room burn through capsules quickly at 250 mg. The forte strength delivers the same total amoxicillin with half the capsules, which usually works out cheaper per treatment course.

Everything else is identical

Same active ingredient, same factory-sealed bottle format, same use cases — fin rot, mouth rot, body sores and other common bacterial conditions in ornamental fish. Both ship from our warehouse in 1–2 business days. See the full Fish Mox overview for what it treats and how it’s dosed, or our plain-English explainer if you’re new to fish antibiotics.