Nitrogen Deficiency
Old leaves (lower) turn pale yellow, then white. New leaves look normal. Whole plant slows down.
Treatment: increase KNO3 dose. Target 10-20 ppm nitrate at weekly reset.
Iron Deficiency
New leaves (top) come in pale, yellow-green, with dark veins visible. Red plants go green.
Treatment: dose chelated iron daily (Fe EDTA or DTPA). Target 0.3-0.5 ppm daily.
Potassium Deficiency
Leaves develop small holes (pinholes), especially in crypts and echinodorus. Browning leaf edges.
Treatment: dose K2SO4 daily. Target 15-25 ppm potassium.
Phosphorus Deficiency
Old leaves turn dark green, then purple-ish. Growth slows. GSA algae appears on leaves (phosphate-starved plants).
Treatment: dose KH2PO4. Target 1-3 ppm phosphate.