Aquarium Plant Fertilisation Guide: Macro, Micro, and Root Nutrition

Aquarium plants require a complete set of nutrients to grow healthy and vibrant. Without the right fertilisation, even plants in perfect light with CO2 injection will develop deficiency symptoms — yellowing, holes in leaves, stunted growth, and poor colour. Understanding what plants need and how to provide it is the foundation of a successful planted aquarium.

The Nutrient Requirements of Aquarium Plants

Plants need three categories of nutrients:

Macronutrients (Needed in Large Amounts)

• Nitrogen (N): Essential for leaf development and chlorophyll production. Usually supplied in sufficient amounts by fish waste (as nitrate).
• Phosphorus (P): Required for energy transfer and root development. Often the limiting nutrient in tanks with few fish.
• Potassium (K): Critical for overall plant health and disease resistance. Often deficient in planted tanks.

Micronutrients (Needed in Small Amounts)

• Iron (Fe): Essential for chlorophyll synthesis. Iron deficiency causes yellowing of new leaves (interveinal chlorosis) — the most common deficiency in planted tanks.
• Magnesium (Mg): Part of the chlorophyll molecule — deficiency causes yellowing of older leaves.
• Manganese, Zinc, Copper, Boron, Molybdenum: All needed in trace amounts.

Fertiliser Options

Liquid Fertilisers (Water Column Feeding)

Seachem Flourish is the most widely used planted aquarium fertiliser. It provides a comprehensive micronutrient profile including iron, manganese, zinc, and other trace elements. Dose 2–3 times per week.

Tropica Premium Nutrition is a complete liquid fertiliser providing both macro and micro nutrients — excellent for heavily planted tanks where fish stocking is low and macronutrient input from fish waste is limited.

Seachem Flourish Excel is a liquid organic carbon supplement (glutaraldehyde-based) that doubles as an algae deterrent. Use in low-tech tanks or alongside CO2 injection to maximise results.

Root Fertilisers (Substrate Feeding)

Root-feeding plants like Amazon Swords, Cryptocorynes, Vallisneria, and Sagittaria extract most of their nutrients from the substrate. Feed them with:

API Root Tabs: Push tablets 3–5 cm into the substrate near plant roots every 3 months. Contains nitrogen, phosphorus, potassium, and iron.

Seachem Flourish Tabs: A comprehensive root tab with 18 nutrients including trace elements. Particularly good for heavy root feeders and plants in inert substrate (gravel or sand).

Building a Fertilisation Routine

For a typical planted community tank:

1. Water change day: Large dose of liquid fertiliser after the change
2. Mid-week: Smaller maintenance dose of liquid fertiliser
3. Every 3 months: Replace root tabs near root-feeding plants

Adjust based on plant response. Deficiency signs mean you need more; algae outbreaks from excess nutrients mean you need less (or more plants to consume the nutrients).

Signs of Common Deficiencies

• New leaves yellow with green veins: Iron deficiency — increase Seachem Flourish
• Old leaves yellow overall: Nitrogen or magnesium deficiency
• Holes in leaves: Potassium deficiency
• Stunted new growth: Could be multiple deficiencies — consider switching to a complete fertiliser like Tropica Premium Nutrition