Whats wrong with my Clams?

[TimT]

If your nitrates are at 0 that is one problem. Clams do need some ammonia/nitrate to fuel their zoozanthellae.

Also check your alk, low alk can cause those symptoms.

Another option is pyramidellid snails, check in the scutes for them and under the clam, around the byssal opening. The snails are generally nocturnal unless there is a heavy infestation.

Clams from Vietnam are also not the healthiest. They tend to carry perkinsus aka pinched mantle disease.

Cleaner wrasses are also known to go after the iridophores on clams. My suspicion is it's a combination of the cleaner wrasse and no nitrate for food.

Cheers,
Tim