I have probably had over 8 various tridacnid clams ranging from derasa to Ultra Maxima. The only ones i've managed to keep alive are a derasa that i've had living for over 3 years (about 6-7" long) and a #1 grade crocea that is at the top of my tank that's been living for almost a year *knock* *knock*. All my water parameters are ideal for the clams but i have no idea why they just die off. My sig describes what filtration stuff i have. Any ideas? I've seen pyramid snails on my clams but i always brush them off about once a week so this can't be the prob.