[danny zubot]

I'm starting to get it.
The sump is baffled so that the level on the skimmer side, also the drian side, doesn't change. The overflow is a 1.5 inch 90 degree elbow with a DYI strainer that determines the water level. When the mysis is added and the water level rises the strainer is completey submerged. Sump level on the other side of the baffles lowers because a) the skimmer has less air and is more full of water. b) tank level is higher.

I think we're on to something with the fatty composition of the food. Could it be creating a back pressure in the drain like you said above? ie. An oily drag on the water going down the drain, thus decreasing drain flow?

What a wierd phenomenon.