Iron is the quintessential micronutrient and the engine of chlorophyll production. Because Iron is immobile within the plant, it cannot be recycled from old tissues. Therefore, a sudden drop in water column iron levels will exclusively strike the brand new growing tips.

Apical and Interveinal Chlorosis

New leaves emerge pale lemon yellow or, in acute cases, completely stark white and ghostly. As with magnesium deficiency, the tissue between the veins fades first, leaving a web-like green vein structure against a white background. However, unlike magnesium (which hits the bottom of the plant), iron chlorosis exclusively hits the extreme top growing shoots. Over time, the white leaves disintegrate and the growing tip dies.

1. Wrong Chelator for your pH

Iron oxidizes into useless rust in water instantly unless protected by a 'chelator'. The standard cheap chelator is EDTA. If your tank's pH is above 7.0, EDTA drops the iron out of solution in hours, rendering it useless to the plants even if your liquid test kit says iron is present.

2. Lack of Micronutrient Supplementation

Depending entirely on fish waste or tap water for micronutrients. Fish waste supplies no iron.

Use the Correct Form of Iron

If your pH is acidic (< 7.0), standard EDTA iron fertilizers are fine. If your pH is > 7.2, you must seek out stronger chelators like DTPA or EDDHA. Some liquid fertilizers (like Seachem Flourish Iron) use Ferrous Gluconate; this is instantly absorbable but lasts only 12-24 hours in the tank, requiring daily dosing. Aim for a maintained 0.1 - 0.2 ppm of Iron in the water column.

Dose your iron or trace element mix daily or every other day rather than in one giant weekly dump. The intense lighting and high oxygen in planted tanks degrade iron extremely quickly. Daily micro-dosing ensures constant availability.