I am having trouble identifying a deficiency can anyone help? Please see the attached picture. Only the top leafs are effected. At first i thought it was a manganese deficiency but after reading i might be wrong. The system is 1 1/2 years old and has been doing great. I add iron, calcium carbonate, potassium carbonate and magnesium. If anyone has an idea and how to correct please tell me. This one has me stumped.