Dosing calculator
Scale any bottle's dose rate to your exact water volume.
Dose for your tank
18 mL
Dose for the water you actually have — substrate and hardscape can displace 10–15% of the printed volume. With medication especially: when unsure, start low and test.
Every fertiliser and treatment bottle is labelled for a round number of litres, and no tank contains a round number of litres — so the everyday question is what fraction of a capful your tank actually wants. This tool answers that, and the number to feed it is the one thing most people get wrong: dose on real water volume, not on the figure printed on the tank. A 60-litre tank with substrate, hardscape and normal freeboard holds nearer 45, so anyone dosing to the label is running a quarter over on everything. For fertiliser that shows up as algae. For medication it is the difference between a treatment and a poisoning, and invertebrates pay first — copper-based treatments have a margin so narrow that a 25% overdose is fatal to shrimp and harmless-looking to the fish beside them. Two more habits worth having. Split large weekly doses into smaller daily ones where the product allows it: plants take up nutrients continuously, and a single weekly slug spends most of the week as surplus for algae to find. And dose after a water change rather than before, or you spend the fertiliser on the drain — a 50% change the day after dosing throws away half of what you just paid for.
Common questions
- How do I convert a dose per gallon to litres?
- Multiply the per-gallon dose by 0.264 to get the per-litre dose (1 litre = 0.264 US gallons). Or enter the bottle's rate exactly as printed above and let the calculator scale it.
- Should I dose for the tank's printed size?
- No — dose for the actual water volume. Substrate, hardscape and the waterline gap commonly displace 10–15%, and heavily scaped tanks even more.
- Should I dose for the tank's stated size or the real water volume?
- Real volume, always. Glass thickness, freeboard, substrate and hardscape typically put a running tank 15–25% below its nominal size, and dosing to the label means overdosing by that much every single time. Work out the real figure once with the volume calculator, write it on the lid, and use it for every bottle from then on.