I agree with CSQ,it's really hard to give a clam to much light. Flow is very important also. Not blasting flow tho just a nice consitant flow. Your T5's should be more then enough as long as you keep up with the bulb changes. Another very important thing is to feed your clams! I know these things you already know just adding a little more is all. I always look for the clams not opening. This is a sure sign your clams having a hard time and look for the start of the tissue separation. If you see these or real change in color as stated then you know it's chowder time.!