This is a good flat worm read link:http://www.melevsree.../flatworms.html
Also have you ever tried the squid bait method for removing flatworms? Here is a quote from "mzoo"
"You may have seen my post from last November...tridacna eating flatworms decimated the 5 clams in my tank in about 4 months. It took me a while to figure out what was going on. I finally caught one on a dead clam shell and confirmed it. I ultimately decided they came in on a new clam.
The medications readily available (flatworm control, flatworm exit, etc.) did not work. I was pointed at some pretty heavy duty medications (IE levamisole) which would have worked but unfortunately can kill fish and I did not want to hurt my beautiful little manadarin goby.
I put raw squid out every week for past 4 months and caught worms on a few occasions. I impaled the bait on a long chopstick and stuck that in the sand. Less than five minutes after lights out, I caught flatworms on the bait and just lifted the whole contraption out, including worms.
They will multiply. They can regrow from pieces. They do eat snails.
I baited, watched at night, monitored my snails, and basically just was very very vigilant for the past 4 months.
After not getting any more on baits, and seeing new baby snails all over, I finally put in a new little maxima two weeks ago. IF I had any worms left, he would have been eaten by now."