Wow, really? I had it for about a month and changing lights has virtually eliminated it. I saw no negative effects. It still grows on the glass a little and there are patches on the sand, but none is growing on the rock or macroalge any more. I can see it would choke corals if you let it sit there, but how could it hurt LR? It never hurt my corals and did sit for quite a while on some hitchhiker cup corals.Brian said:I'm no expert on the stuff but the result of leaving it unchecked is it can virtually disolve corals and or liverock it comes in contact with. It's nasty stuff