Reading the threads on this forum after researching the heck out of this topic, I have decided to nuke my planaria infested tank and just break it down and throw everything away. It's a 10g quarantine tank that evolved into a planted tank to make snails for my pea puffers (who are absolute snobs and refuse to eat anything frozen and only like live baby brine or live rams horn snails). I only kept a couple of baby plecos and a bunch of snails with lots of plants in this tank. I suspect they hitchhiked on 2 pieces of wood I bought from the aquariums at Petco. It happens...
At first, when i saw a few of them, I didn't mind (I thought this would just be free food for the plecos).
But then... fish started to disappear. At this point, since the planaria showed up, my fish just vanished. So far I have lost 4 small plecos and 7 of the 8 guppies I added in the hopes that they would eat the planaria. I only ever saw one dead guppy in the bottom of the tank on my way out of the house when I was in a rush, came back home about 3 hours later and went to remove the dead body and there was no trace. That has been the case for all the fish in there that have simply vanished without a trace. I suspect the snails have been very efficient at disposing of the bodies.
Regardless, I'm done. Will remove the fish that are left and throw everything else away except for the air pump and heater (plants, sponge filter, wood, substrate, even the air tubing). I don't even want to keep the tank itself. I considered dosing the tank with the planaria remedies but I am so disgusted by the whole thing and don't want to risk transferring these critters to any other tanks.
I hate them!