If there is one thing I am proud of myself in this hobby, is defeating these little red *******s!
I had them in my 75 gal covering entire rocks, the sand, and even on corals... it was getting really bad!
So I tried the flatworm exit medicine, followed by a 100% water change. You could see the worms dying and thousands floating around in the water column.
So, the medicine worked. BUT, as ppl here have mentioned... a couple of weeks later everything was the same. I repeated this procedure like 3 tmes.
Finally I was about to give up, but someone suggested I get an african Black Leopard Wrasse (a hard fish to keep), and I was willing to take the risk. I put two of these in the tank along with a small coris wrasse I (cause I thought he was cute).
In maybe 2 weeks there was not a single flatworm in sight!!!!! It was the most spectacular thing I had ever seen! Now, I dont know if it was the leopard wrasses or the coris wrasse... I actually never saw them eating a flatworm... but man, I'm telling you, from rocks and glass and sand COVERED in red, to ZERO flatworms.
So I would say try with a small coris wrasse (or a couple of them), see how it goes, if they fail, get those african black leopards. It can be done!!! you can do it!!!