unfortunately, i can tell you that you don't have sufficient lighting for your clam, especially if it's a crocea (hard to tell if we can't see the shape of the shell and its incurrent siphon, as Renee mentioned.). if i had to hazard an educated guess, i'd say it's a maxima, as croceas tend to be quite a bit more "gapy", especially in a new system. without the intense light of
MH, the clam will most likely bleach over time and die.
at this point, the best thing you can do in your system is to get the clam as high in the rockwork as you can so it's as close to the lights as possible.
also, clams hate flow...if their mantles do more than gentle lifting, the flow is too much. they typically won't extend their mantles if this is the case.
keep your
Ca at about 450...at LEAST 400. also, they don't tolerate heat very well...so keep the tank below 80.
since clams have a fully developed digestive system, and since your lighting is sub
par, you'd do well to feed the tank with live phyto such as
DT's...your coral will appreciate it as well.
if you have any angelfish or butterflies, there's a good chance they'll nip at the clam's mantle. dwarf angels such as the coral beauty can be especially problematic since they feed on the mucous of clam mantles.
all that being said, i see a lighting upgrade in your future if you want to keep the clam.
ryan 
icon under their name to add to their reputation. 
