Wow! Not only does this thing work, it is very powerful. I got this, to create some water movement, in my 40 breeder. I chose this size (the 317gph), based upon it being about 8x the volume of my tank. Based upon the research I did, you want to turn your tank's water 5-10 times per hour. I put it in the tank, turned it on, and it started blasting water. My plants were getting ripped out of the substrate (some of them, and they haven't had a lot of time to develop a good root system, yet), and my fish were fighting plenty of current. For a larger tank (maybe a 75 gallon), this might be the right sized pump. I actually ended up buying another pump, with half the gph rating, to use in my 40 breeder, and it creates just about the right amount of water movement, for my tank. Keep in mind, I have some fish who prefer medium-fast water movement (zebra/glo danios, harlequin rasboras, pictus catfish), and some who like medium-slow movement (rams, dwarf gourami). I would definitely recommend these pumps. It is nice that you can swivel the output, to point it where you need it, rather than just straight out from the wall. They have plenty of power. Just, make sure to take that into consideration, when choosing the size you want to buy. As with many other purchasers, I am confused as to what purpose the flexible plastic hose, which comes with it, is supposed to serve. At first, I assumed it was meant to move the intake or output, to somewhere other than where you stick the pump. It does not fit on either the intake or output nozzle. It will fit on the smallest "step" of the intake guard piece, but what good would that do? I also thought, maybe it is for water changes, but it is not nearly long enough, to be useful for that purpose. Although, these pumps are great for water changes. Just get some 5/8" inner diameter tubing, and stick it on the output nozzle.
