Not sure if this was the right forum to post this but I have these brown spots on some of my softies and I thought nothing of them till I say them move they are a live and moving. Seems to be some sort of slug.
those look like flat worms, they can spread to plague porportions very fast!
a better picture would help ID them for sure. take some airline hose and start a siphon and see if they will suck of the corals and rock with the airline hose if they do they are flat worms....
They are flatworms. Search out "flatworms" and you will find the info you need to remove. Anything from "cleaner" animals to some pretty harsh chemicals.
It is hard to tell from the pictures, but they may be a kind of jellyfish (sessile ctenophore). How big are they? Do you see them on anything beside softies? Do you ever see long filaments extending from them?
If they are ctenophores, they are harmless and interesting.
I believe 6 line wrasses(and a few others) eat flat worms . Assuming thats what they are--the picture is kinda blurry do you have a tripod to help hold it still ?