I'd say you either need t-5 or a small MH. I have a 16g nano, with a 175w MH and 2 12" VHO, and I keep 2 clams. a 5 inch gold T.max, and a 4 inch crocea. I think your lighting would be fine for a derasa clam. The biggest thing your going to have to deal with is the Calcium and ALK swings. If I was you, I'd get a mature Derasa clam for your first one. Like SMCNALLY said, baby clams are alot harder to keep, they are more likely to up and die from a small swing in params, or from being underfed. Baby clams arn't as photosynthetic as their bigger brothers.