How Much Treatment Does Your Tank Actually Need?
Pick a verified product or enter any label dose, multiply by your true water volume, and get the exact amount to measure — in milliliters, teaspoons or packets — with the manufacturer label as the always-current authority.
Your dose
Frequently asked questions
How do I calculate a fish tank medication dose?
Multiply the label dose per gallon by your net water volume — the actual water in the glass, not the tank name. If the label says 5 ml per 10 gallons and your tank truly holds 18 gallons, you need 9 ml. Dosing by the nominal tank size overdoses by the displacement of substrate, decorations and the air gap.
Why does this calculator show a check date on each product?
Because manufacturer labels change. The built-in products are read from the manufacturer's own product pages and carry a verification date; if a formula is revised, the label wins over any calculator on the internet. Treat the table as a convenience and the bottle in your hand as the authority.
Is 5 ml the same as one teaspoon?
Almost — one US teaspoon is 4.93 ml, so a 5 ml dose is just over a level teaspoon. Kitchen spoons vary, which is why the calculator shows both readings. For medications where being slightly off matters, use the measuring cap that comes with the product or a syringe.
My product is not in the list — what do I do?
Use the label converter lower on the page: find the per-gallon dose printed on your bottle, enter it, and multiply by your net gallons. The converter does exactly what the label says and nothing more — it does not guess at concentrations, courses or repeat doses.
Should I dose for the whole tank or just the new water?
Water conditioners (dechlorinators, stress coat) follow the water you are adding: dose for the change volume. Medications, by label convention, almost always dose the full aquarium volume because the active compound needs a stable concentration in the whole system. When in doubt, the label states which caliber it means.
How do I dose powder medications like General Cure?
API General Cure calls for one packet per 10 gallons of aquarium water, repeated after 48 hours, with a full course being both doses — one retail package treats 100 gallons. Dissolve the powder in a cup of tank water first and pour it in gradually; dumping dry powder straight onto fish stresses them.
Do I need a separate dose for chloramines?
Yes for standard tap water conditioners — removing chloramines takes more product than removing chlorine. API Tap Water Conditioner, for example, calls for 1 ml per 10 gallons against chlorine but 5 ml per 30 gallons against chloramines. If your water utility uses chloramines (many do), use the stronger figure.
Can I overdose a water conditioner?
Conditioners like Stress Coat and Prime are deliberately forgiving — a modest overdose is harmless to fish. Medications are not: antibiotics and antiparasitics scale with volume, and doubling a course to speed things up mostly stresses the fish and the filter bacteria. Follow the label, dose by true volume, and complete the full course.
Sources & rule confidence
Every rule baked into this calculator traces to a community source and carries a confidence grade. A = multiple independent community confirmations; B = consistent direction, edge cases remain; C = direction only, numbers are reference values. We show disagreements instead of hiding them.
- R3 · A Dosing follows the manufacturer label (manufacturer-fact): API Stress Coat 5 ml/10 gal; API Tap Water Conditioner 1 ml/10 gal chlorine and 5 ml/30 gal chloramines; API General Cure 1 packet/10 gal, repeat after 48 h, one package treats 100 gal (verified 2026-10-17).
Every built-in product dose is read from the manufacturer's own product page (apifishcare.com) and re-verified — the table shows each product's check date, and the label on the bottle always wins over any calculator. Products not in the table are handled by the label converter: multiply the printed per-gallon dose by your net water volume.
| Product | Label dose | Manufacturer source | Verified |
|---|---|---|---|
| API Stress Coat | 0.5 ml/gal | API Stress Coat product page | 2026-10-17 |
| API Tap Water Conditioner | 0.1 ml/gal | API Tap Water Conditioner product page | 2026-10-17 |
| API General Cure (powder) | 0.1 packet/gal | API General Cure product page | 2026-10-17 |
Disclaimer
All figures are estimates for freshwater community aquariums and do not replace the product label, a water test kit, or professional advice. When a rule on this page is graded C or marked estimate-grade, treat the numbers as an order of magnitude, not a target.