corrode??? no....... but juz an eyesore. my fishes r smart enuff to know those styrofoam bits r not food. no problem wif sponges, but beware ur bubbles kanna punctured, LRs topple, etc......
maybe can try sun coral as well. they dun require much lights....... i put the sun coral in a shaded region of my reef tank. so far so good. but they need target feeding on each polyps.
If u hv a styrofoam made backdrop in ur tank, my advice is NEVER HV A URCHIN IN UR TANK!!! That was the mistake i hv made. the urchin will crawl all over the shop and drag its spines against ur backdrop till u can c lots of tiny styrofoam bits floating on the tank surface and clogging ur filter wool!
right on bro roidan!!! i got those damn red slime in my refugium. got them due to overfeeding of GPs in my tank. best way of removing it IMO would be to do a partial water change.