The short answer
Start with the dose on the bottle for your tank’s volume, then adjust based on what the plants tell you. There’s no universal number — the right amount rises with more light, CO2 and fast-growing plants, and falls in a low-tech tank of slow easy plants. Dose consistently, watch the plants, and change one thing at a time.
A sensible starting point
Every all-in-one fertiliser prints a dose per volume — usually a capful or a number of millilitres per set number of litres, once or twice a week. Use that as your baseline. In a low-tech, no-CO2 tank, start at or below the recommended amount, because slow plants can’t use much and the surplus feeds algae. In a high-light, CO2 tank, plants eat far more, so you’ll likely dose the full amount and often more.
Read the plants, then adjust
- Pale, stunted or holey leaves → the tank is short of nutrients: increase the dose gradually.
- Healthy plants but algae creeping in → you may be over-lighting or over-dosing relative to what plants use: ease off or shorten the photoperiod.
- Strong, steady green growth → your dose is right; leave it alone.
Give any change two to three weeks to show in new growth before adjusting again. See our fertiliser picks and the fertiliser hub.
Don’t forget the roots
Water-column dosing feeds most plants, but heavy root feeders — swords, crypts — also want root tabs in the substrate, replaced every few months. The liquid vs root tabs guide explains the split. And remember fertiliser is only one leg: match it with the right light, and CO2 if you’re running a high-tech tank.