And sorry about your Maxima, Ann - I hate when stuff like that happens.

 

Sometimes you never really figure out why...

 

 

 

Anyways, I think it's time this thread was dropped since it's no longer productive and the cause of the clam's death is not going to be found out at this point. Thanks everyone for your help!

Mark, as Nikki said, I am running plenty of lighting in a good color spectrum and get great growth and health out of my corals as well as another Tridacnid. If starvation were the issue it would have shown earlier in an algae coating on the sell and by an absence of new growth (thus the algae on the shell). If temperature were the issue the bleaching would have started long ago since the temperature has always been maintained at 78-80F (78 at night, 80 during the day). The clam was perfectly happy and healthy up until about 2 days ago. I'm by no means an expert, but have done my fair share of research on clams and can say this was not a common problem that people encounter. The problem with diagnosing clam deaths is that they often seem to occur quickly and without warning. However when we examine these "mystery deaths" it soon becomes apparent that there were warning signs such as a lack of growth, bleaching, retraction, gaping, etc. However, none of these signs appeared until approximately 36 hours prior to the clam's death, leaving most of the common problems such as starvation, temperature, pests, etc. almost out of the question.

Nikki, I agree it was likely some type of bacterial or protozoan infection. It seems the only likely explanation given the circumstances and symptoms shown.