I have seen people us a dewoemer med for dogs to treat planaria. Would this working in this instance?
Yes. it probably would, Flubendazole is often adviced (Flubenol 5%).. It's also used for Gil and skin flukes. Tho, it is a med that administered orally to animals, it is not developed to dissolve very good into water. As most of the usual deworm pet meds are.. Planaria is a resiliant bugger, the adviced dose Flubendazole against planaria is 2 gr/100L and that is quit a high dose.. No warranty all fish will take it very well, for skin and gil flukes a 0.8 gr / 100L is adviced and still with causion.
So for treating against planaria with delicate tropical fish in the tank it is quit an agresive method. A more safer option is <NoPlanaria>, this is a Beetlenut extract that is safe for fish and shrimps and definively kills planaria and unfortunately some snails as well.
Still need to be very causious, since you do not know how many planaria you have killed that are in the substrate. Seeing one or two, means you might have 100x as much you don't see.. Doing a lot of extra water changes and substrate vacuuming after the treatment realy is a nessecity. If you don't you might run into trouble because a huge bioload of dead and rotting worms in the substrate can releas a lot of nasties into the water column killing the shrimps and sicken some fish.
Obviously this goes for any alternative treatment that kills them.