The short answer
Yes — most planted tanks need fertiliser sooner or later. Fish food and waste provide some nitrogen and phosphorus, but they don’t supply the potassium, iron and trace elements plants need to thrive. A small collection of hardy plants might coast on fish waste alone, but a proper planted tank grows far better with a regular all-in-one liquid fertiliser.
When you can skip it
If you have just a few tough, slow-growing plants — Java fern, Anubias, mosses — in a stocked, fed tank, they may get enough from the water as it is. These plants barely draw on reserves, so they tolerate lean conditions. The moment growth pales, stalls or develops holes, that’s the tank telling you the buffet has run out.
What kind of fertiliser
For most tanks, a weekly all-in-one covers every nutrient in one bottle and keeps dosing simple — see our fertiliser picks and the fertiliser hub. Root feeders such as Amazon swords and crypts also appreciate root tabs pushed into the substrate near their roots. The liquid vs root tabs guide explains which plants want which.
How much and how often
Start with the bottle’s recommended dose for your tank volume and adjust from there — pale, slow plants want more; algae creeping in with healthy plants may mean you can ease off. For the full method see how much fertiliser to dose. And remember the other two legs of the stool: enough light and, for demanding plants, CO2.