clam expelling zooxanthellae

[Will]

my 2" squamosa has been doing great for going on six months now. as of yesterday, it appeared to not be expanding as much as it has been. today i noticed a trail of dead zoox coming out of its exhalant siphon. what could this be signifying? i've also got a 1.5" maxima that's doing great... i really haven't changed much in the tank lately. i upgraded from PC to MH lights about a month ago, but everything came through looking better than ever. is this possibly a delayed reaction to that? i'm at a loss.
fourhand2

[Nuuance]

I'm no expert on clams by any means, but I have read that clams will sometimes expel excess zoo, possibly for a variety of reasons. Perhaps the upgrade to MH lighting is simply producing more for the clam and it is going through an adjustment period, especially given the size of the clam. Younger clams are known to better control the levels of their symbiotic algae.

Hopefully someone that knows more than me about clams (just about anyone here), can better assess the situation and answer the question.