Manganese (Mn)
A plant micronutrient that pairs with iron in most fertilisers. Rarely deficient alone, often the missing partner when iron dosing "isn't working".
What it is
Manganese is a trace metal plants use in chlorophyll synthesis and in several enzyme systems that handle reactive oxygen species. It pairs with iron functionally — most planted-tank "Fe" deficiency symptoms are actually combined Fe + Mn deficiencies.
Why it matters
Pure iron deficiency is rare; what most aquarists call iron deficiency is the broader micronutrient deficiency that complete trace mixes correct. Most commercial micro fertilisers (Tropica Specialised, Aqua Rebell Mikro Basic Eisen, Easy-Life ProFito) include manganese alongside iron specifically because dosing iron alone gives partial colour recovery but not full growth recovery.
How to test
JBL Mangan or similar kit. Manganese sits in the 0.05–0.5 mg/L hobby range; most aquarists don't test it routinely and trust that a complete trace mix maintains the ratio.
What high and low look like
Below 0.05 mg/L sustained: chlorosis with green veins on older leaves, similar to magnesium deficiency but with smaller pinholes. Above 1 mg/L: not toxic but unusual; means a trace mix has been over-dosed.
How to fix
Switch from a Fe-only product to a complete micro mix that includes Mn, B, Cu, Zn, Mo. The dosing rate is the same as for iron alone — typically 1–2 mL per 100 L every other day.
