FLATWORM, just read a post the other day and "KIP" said that those clear/white ones are harmless and the bad flatworms are a red/brown color. Maybe do a search to find the post but that is the info. I read, they should be fine.
Well i had those in my 12 gallon and i heard that they reproduce like crazy and if a large amout die at one time it will kill everything in your tank. So what i did like everyday till i didnt see anymore is I would wait like 2 hours after the lights went off and use a flashlight and shine it on the glass and if I saw one I would suck it up with a eye dropper and dispose of it. HTH
So far, I've only noticed them in my refugium. It must have come in as a hitchhiker on a LR purchase. There are three on the front glass, so there are probably many more, but I think they will stay in the refugium for now.