Thinking of adding a small rock clam like a maxima to my 13.5g tank. Total water volume once my third tank is hooked into the system will be closer to 40g. 2 13.5g fluvals, 1 16.5g tank, and 1 20g sump. How much calcium realistically would I need to supplement for the clam to thrive? Do you guys thing a 5g water change weekly would be enough to keep it happy or would 2 part supplements be needed?