the UV sterilizer didn't do it, so you can rule that out. it's only good for parasites in the water column.
actually, there is controversy about whether a UV sterilizer is any good for a reef, since we want planktonic creatures and pods to flourish, and anything that passes through the sterilizer is killed (i don't know if it works on bacteria though, and if it did, you'd have to get it all to go through the device)
627, i would consider removing it.