I have the prism skimmer, and I know the exact slime surface build up you mean. I bought the add on piece and as long as you us it correctly and don't mind the size, which is actually quite a bit larger than the origonal tube it works well. I do tend to aim one of my powerheads towards the surface anyway, cause as water evaporates it tends to decrease how well it works. Keep track of your water level and and you should be good.
