From you pictures it looks like you have it on the bottom? My understanding has always been that Maxima prefers to be on the rock work, esp the Blue's that need more light than the green or browns and prefer to be higher up.
What type of MH
do you have? wattage and K
Blennies have also been known to be agitators of clams
Do you spot feed, or feed at all w/ zoo & phyto plankton? Or does he just rely on filtering and photo?
Does he close up rapidly when you get near him? How's the mantle look?
What was the nitrate reading? Some nitrates are good for clams.
I still think you're close to the edge on stocking.