The black algae on the plants is probably the beginning of Black brush algae, a sign of not enough CO2. The green may be green spot algae, a sign of not enough phosphate. See, excess ferts don't cause algae, but shortages do. PMDD doesn't contain any phosphate, so unless you dose it separately you will always be short of it. And, if you are short of phosphate, the plants can't use all of the nitrate, which is in short supply in PMDD.