i would not have put sand in the fuge...that appears to be a very low flow fuge, and it is fed dirty water from the tank, you are going to have piles of poop settling out in there, and a tonne of nitrate problems to go with it...
as for your foaming rock tower, you have a air water drain that also has a Y fitting in it that adds considerably more turbulence to the drain...and now you are splashing this air filled water all over a pile of rocks...it is certainly going to foam up, you are basically creating a very primitive skimmer out of your rock tower...
i like the rest of the setup though...looking good.