I do clean alot, being a discus tank I do about 25% water change every 2 - 3 days and syphon each time I do. There is no algae on the glass and the snails are just on basically every plant (even the small floating ones?!)
I'm going to worm my discus this week, my first time doing it and apparently the stuff is pretty bad for snails, so maybe this will help?
As for the assains eating each other, I had never heared of it either. At first I thought they where mating so I kept a mental note of what part of the tank they where in and checked back the next day. So far I have spoted them doing it 4 - 5 times and have now found 3 empty assain shells in less then a month.