I have let my tank go too **** ! I was busy putting a deck and siding on and all I did was add kalk to the tank. I got a major dose of red slime algae ,it is about 1/2 cured through water changes, and I replaced my flourescent tubes thinking it was a light spectrum change. I still have some red algae,and there is a layer of something on the surface that clogs the overflows. It is kind of a solid crust like excess calcium, but my cal level is only 425-450. The pump in the sump looks like it is blowing out air bubbles but whatever they are is the cause of the problem I believe? Anyone have any ideas?