Once an evil evil arrow crab ate my 3 Sexy shrimp in one evening. Revenge was sweet
The reason I suggest fish as a cure is that myself & a friend had what you would refer to as a "controlled" flatworm infestation. More of an experiment, we were able to keep a colony of flatworms alive in both of our tanks by placing a fist sized piece of rock against the glass with the flatworms growing on the glass agaisnt it. As soon as they reproduced beyond the shelter of the rock, my 6 line wrasse & his arceye hawkfish would devour them. About a week later while at a LFS, I spied a sad, skinny mandarin & convinced them to let me take it home for free & see if i could nurse it back to health. It would have died in another 2 weeks so they said what the hell & let me have it, since it was so skinny & ugly nobody was going to buy it.
I put the mandarin & my tank & it gravitated to the rock against the glass. Since it was approx 3x longer than my 6 line, the wrasse was sufficiently intimidated to move away & let the mandarin have at it. The mandarin Chowed Down on flatworms for days. After 2 weeks it had gotten its belly back & looked really nice. Too bad for me that my roomated cleaned the glass & moved the flatworm sanctuary rock away from the glass. I got home from work that night & all the worms were gone, the mandarin pecking aroung my tiny 15 gallon tank looking really dijected.
I called my friend, told him what happened & he moved his wormhaven away from the glass. The next morning all of the flatworms were gone.
Arceye hawkfish, 6 line wrasses & mandarin gobys eat flatworms. I seen it with my own eyes. Arrow crabs will kill & eat your small shrimp, I've seen that too.
I returned the mandarin to the LFS & I'm sure they sold to to someone who watched it starve to death over the course of a month.
regards