hmmmm interesting! there's noticeable effect on the nitrate & phosphate levels, could be the BB at work too? I don't know if it makes sense to dose coral food, monitor the levels then, & then one day later... That can also tell how much they are cleaning your water? Will that work?
otherwise is just monitor for more days with no skimmer & food to see if they can reduce the levels even further..
Bro your clams are your tank's natural skimmer