bio filter ,pollen and crust

I built two sand filters this winter and have come up with two problems. First is for some reason a crust forms on the sand and stops the filtering. it really hasn't been warm enough to form the bio mass on top.

Second is the pollen. The water had been nice and clear. (I heated it for use for bah and dishes, dont drink it) But with the spring blooms pollen in the water (leaves a yellow ring around the primary catchment) has caused the water to turn a light yellow. Ok or bad ? Your ideas?? and should i use the yellow water

My understanding (lots of research, no actually DOING yet) is that the biofilm is what eats the junk off the top and slows the plugging, but you still need to rake and drain the sludge off occasionally.

Shouldn't be getting color through a slow sand filter if the biofilm is working correct. Definitely don't drink yellow water!