They can be made to work, but they are fussy and problematic. They do require a perfectly constant level of water, and theelbows are prone to leaking or breaking. Pumps are not the best but they do work. Lots of folks swear by them and lots of folks swear at them. Personally if yu can not keep a constant level in the sump or tank, I would consider a Lee's or Sanders air powered skimmer over the Fission skimmer. Those two skimmers at least do work as long as you keep the air diffuser clean.