I'll agree. The filters are washable. I've been washing mine after
buying the third Econo-box of em'. Just run water over the filter while
brushing the media with you hand. I can get 3-4 runs out of the same
media if I am gentle.

You will probably find the green slime is Cyanobacteria aka Blue-Green
Algae. The stuff grows fast to consume extra nutrients. BGA carries out
photosynthesis (which explains their green color). If you eliminate
light entering the filter, You eliminate the BGA (or most of it)......
Oh, I don't think the stuff is necessarily bad for the tank. It doesn't
foul the water so far as I know. It just looks bad and clogs filters

My Aquaria info & pics at:
http://www.geocities.com/spiral_72/Spirals_page.html