T. Crocea is one, if not the most, light demanding of all the Tridacna clams. I would really only put them under a halide unit; is this something you have on your setup? A little description of the setup would be helpful. Sorry not been in for a while but do remember you started a smallish nano??
Anyway another thing with Tridacna in general is try and get a specimen that is 4 inches or bigger. This is because below roughly 4 inches the clam's mantle is too small and they have very immature vascular systems therefore it is hard to maintain sufficient nutrition. I had a small maxima that was an inch long and within two-three days it was dying. It was maybe 8 inches from the water surface within a 150 watt halide above it!! Normally they a cultured in an inch of water in direct sunlight in places like Hawii. Apparently the PAR is sometimes as large as 10,000 which is really expensive and difficult to immitate in an aquarium. If you get a 4 inch clam then they are frequently ok under 150 watt halide. The only thing I would say is that they generally like moderate flow not the crazy fast flow that many SPS enjoy so think about location of the clam and species of SPS as to maximise success.
Hope this helps
Joe
