Croceas are the most light needy of the giant clams. According to everything I've read they should only be kept under MH
lighting. I know from personal experience that they can take all the light you can throw at them, and some, and will love it! A Derasa or Squamosa clam would be more appropriate under your lighting.
Jason 8 months is not along time at all. It will some times take upto 6 months just for clams to start showing signs of stress due to poor lighting/water quality. HTH