I would have to agree that Croceas are more light demanding than other clams, and I would not suggest one for a first time clam keeper, mabey a captive bred Squamosa or Derasa. Actually no clam is easy to keep, but captive bred clams will not only give you a better chance at success, but if it does happen to die, at least it wasnt taken from the ocean. I think a 175 would be fine for most sps and clams, of course there are always those clams and sps that do best under more light, a 250 would be better, heck if you could do it a 400 would be optimal for sps and clams, but I think heat will be an issue with all MH on a tank of that size. GL