Iron and manganese toxicity on geranium

The symptoms on this geranium are due to iron and manganese toxicity, a nutritional disorder associated with low growing medium pH (below 6.0). This problem is sometimes called "bronze speckle" due to the numerous small brown spots on the leaves. Zonal geranium, American marigold and all types of impatiens are susceptible.

Fact Sheets
Basic Fertilizer Programs for Containerized Greenhouse Crops
pH and Fertility Review for Vegetatively-propagated Annuals