The picture attached is of leaf damage to older/lower leaves on three plants in a well established 150g aquarium. I am certain it is a deficiency of one or more key nutrients. I have begun using PMDD and am sure it will be corrected by that, however for my own information, I am wondering what the deficiencies were?

I have consulted this link Nutrient Deficiency in a Planted Tank and would guess potassium, but several symptoms appear in multiple entries.

I believe it was dosing with only Flourish Excel that resulted in this deficiency as I have not had problems previously. I was under the presumably mistaken impression that Flourish Excel was a comprehensive nutrient source.

Michael