Fertilizing a planted tank is less complicated than the internet makes it look. Plants need a handful of things in reliable supply, and most problems come from one of them running out rather than from a subtle imbalance.
What plants actually run out of
Nitrogen, phosphorus and potassium are the macronutrients, needed in quantity. Iron and the other traces are needed in small amounts but run out fast in a tank with strong light. Carbon is usually the real limit, and that is what CO2 injection addresses — no amount of fertilizer compensates for a carbon shortfall in a high-light tank.
The symptoms are readable once you know them. Pinholes and yellowing on older leaves usually point to potassium. Stunted, pale new growth points to iron or another trace. Older leaves yellowing evenly and dropping points to nitrogen. Plants that simply stop growing in a bright tank are usually short of carbon, not nutrients.
Liquid, root tabs, or both
Liquid ferts feed through the water column and suit stem plants, epiphytes like Anubias and Bucephalandra, and floating plants — anything not rooted in substrate. Root tabs feed heavy root feeders directly: swords, crypts and most bulb plants. A tank with an active aquasoil already has a nutrient reserve in the substrate and needs less of both early on; an inert sand or gravel tank needs more from day one.
Dose for your tank, not for a chart
Published dosing schedules assume a light level, a plant mass and a CO2 setup that are probably not yours. Start below the recommendation, hold it steady for a few weeks, and change one thing at a time. Chasing symptoms by adding a new product every week is how people end up with algae and no idea which bottle caused it.
Bring in a photo of the tank and we will tell you what we think it is short of.
