The short answer
Aquarium plants need two groups of nutrients: macronutrients — nitrogen (N), phosphorus (P) and potassium (K) — which they use in large amounts, and micronutrients — iron and a set of trace elements — which they need in tiny quantities but can’t do without. Plus carbon, which comes from CO2. Supply all of these in balance and plants grow green, strong and algae-resistant.
The macronutrients (N, P, K)
These are the heavy lifters:
- Nitrogen (N) — drives leaf and stem growth. Shortage shows as yellowing, dying older leaves.
- Phosphorus (P) — energy and root development. Some comes from fish food and waste.
- Potassium (K) — regulates many processes; a common shortfall in fish-only tanks, often seen as pinholes in leaves.
Fish waste and food provide some N and P, but usually not enough K, which is why dosing helps.
The micronutrients (iron and traces)
Needed in minute amounts but essential:
- Iron (Fe) — vital for chlorophyll and rich colour, especially in red plants. Deficiency shows as pale new growth with green veins.
- Trace elements — manganese, zinc, boron, copper, molybdenum and more, each playing a small but necessary role.
Carbon and how to deliver it all
Carbon — from natural CO2, injected CO2, or a liquid carbon supplement — is the other big input. Faster-growing, brightly-lit tanks demand more carbon and more nutrients; low-light tanks need far less of everything.
- Water-column dosing — liquid fertiliser feeds leaves and stems.
- Root tabs — pushed into the substrate, ideal for heavy root-feeders like swords and Cryptocoryne.
Match your dosing to your light and CO2 so plants, not algae, use the surplus. For more, read how much light aquarium plants need and CO2 for beginners, and browse the full fertiliser hub.