Aquarium plants tell you what they are missing. The trick is knowing where to look: nutrients that plants can move (nitrogen, phosphate, potassium, magnesium) show deficiencies in old, lower leaves first, while those they can’t move (iron, calcium, most trace elements) show up in new growth.
Old leaves turn yellow: nitrogen
The oldest leaves yellow evenly and the plant grows slowly. Common when nitrate is below 5 ppm in a well-lit tank.
Fix: dose a macro fertilizer containing nitrogen (for example potassium nitrate), aiming for 10–20 ppm nitrate.
Small holes in older leaves: potassium
Pinholes that grow larger, often with yellow edges, on older leaves. Very common because potassium is used up quickly.
Fix: add a potassium supplement or a complete fertilizer.
Pale or white new leaves: iron and micronutrients
New leaves come out pale yellow or almost white while the veins stay green. Red plants lose their color.
Fix: dose a micro (trace element) fertilizer with chelated iron. Dose little and often; iron breaks down quickly in water.
Green spot algae and stunted growth: phosphate
Old leaves get dark or develop green spot algae, and growth stalls even with enough nitrate.
Fix: keep phosphate around 0.5–2 ppm in planted tanks with a phosphate fertilizer.
Twisted new leaves, weak stems: calcium or magnesium
Deformed new growth usually points to very soft water.
Fix: raise GH to at least 4–6 °dH with a remineralizer (GH booster).
Slow growth everywhere: CO₂
If everything grows slowly and algae appear on leaves, CO₂ is often the limit, especially under strong light. A drop checker should be light green (about 30 ppm).
Fix: add CO₂ or reduce the light so the plants’ demand matches what is available. Our algae guide explains the balance.
Root feeders
Amazon swords, cryptocorynes and other rosette plants take most of their food from the substrate. In plain gravel or sand, push root tabs next to their roots every 2–3 months.
If you keep shrimp
Choose shrimp-safe fertilizers without copper, and dose gradually. Shrimp react badly to sudden changes in water chemistry.
Fishtify knows the needs of the plants you add, suggests a fertilizing task schedule and checks your nitrate against the range your plants need.