[Tanuke]

I have had a brackish 5 gal. opae ula tank going since June. It has live sand and lava rocks (not live rocks), and a sponge filter going at a very low bubble. I was told by the Hawaiians I got the shrimp from that they don't like filtration since they normally live in ponds and lava tunnels/caves. The shrimp seem to be doing just fine but there's this greenish-yellow stuff (looks like slime) "growing" on all the sides, rocks and sand. Is this algae gone wild? Or is it really slime from some inbalance? The shrimp sometimes feed on it but there aren't enough shrimp to clear it away. Should I scrap it off as best I can? All winter I've only been feeding the shrimp a pinch (literally) of powered spirullina once a week so it can't be from overfeeding. Is there anything else I can do? The tank does sit on a bookcase in front of a window but it's got a background sheet on 3 sides, and the tank light is only a 15watt incandescent bulb. Advice and suggestions? I want to disturb the shrimp as little as possible since this is their breeding season.