Unsure, myself, but I do know that bivalves - especially filter feeders like scallops, clams, and mussels - tend not to thrive long in ultra-clean or low-nutrient reef systems, because they rely heavily on suspended particulate matter, phytoplankton, and microfauna in the water column to feed. In sterile or heavily skimmed tanks with high filtration and minimal dissolved organics, their food supply is often insufficient unless intentionally supplemented.
A lot of folks who successfully keep these and other filter feeders either usually skip a skimmer entirely, or tend either to turn it off for a few hours after dosing phyto, etc., or only run it at night. If you've got a fuge, periodically hitting it with a turkey baster to blow the crud off the macro or rocks and allowing it to circulate in the tank also would help ensure they have plenty to eat.
