I have a couple of varieties in the tank but they share a common problem. It may take a couple of weeks and some may not be so susceptible but they appear to be getting smaller in size. Water changes are done regularly and the ph is at .023-.024. Lugols is added once a week (3 drops per 75 gals) and they're spot fed once a week with pumps off. They have about 4 watts/gal and placed midway up in the tank (power compacts). Calcium is also added - approx. 10-15 cc's once a week although a calcium hasn't been checked in some time. I'll check the Ca level but any other suggestions???