I've been doing some further reading on it and it might be Riggia cryptocularis but found this:
"In aquaria isopods rarely cause any problems. The chief exceptions are cirolanid stowaways in marine aquaria which may attack fish, and the occasional cymothoid parasite imported with catfish, especially Otocinclus. Cymothoids are nasty, but I've never heard of them spreading in aquaria."
Then I remembered the post last night about the oto who looks like it swallowed a marble...