Hi Matt, I found fungia a bit hard to keep myself ,I love that there are so many colour forms too.
Was still thinking about your clam loss and you are not going to like this suggestion from DD
" clams are very susceptible to attack from bristle worms , especially when positioned on a sandy or gravel substrate. If you have had clams die in the past this is proberbly why. The worms attack the base of the clam at night and slowly eat it out from the inside."