I've been fighting this for a while but am still struggling. I've added iron and that seems to help for a very short bit then the same thing happens again. Have added potassium via Kelp tea and banana peals in GB. Still no go. These plants are also growing slow, although my tomatoes seem to be doing just fine. Please Help??  My system is a 600 gallon system with tilapia, goldfish and bluegill. w…