They work well. Although they are hard to keep track of unless you have no fish, shrimp, or other invert predators. I kept mine in a tupperware container in my sump and put rock in it for them to clean. Well you know, while I had that going on I bought some peppermint shrimp and put them in my main tank with tons, I mean tons, or aiptasia and now the aiptasia are all gone. The peppermints are really what took care of them I believe. I never fed the shrimp a single thing so I guess they resorted to aiptasia, thank God!!!! (seriously)