I have run the Hydor Wave Maker in the past. What happens is that sometimes, the pump doesn't turn on, or sometimes it runs backwards, and once in awhile it pushes water forward like it's supposed to all the time. There are many obvious problems with this defective Hydor pump. However, nothing is worse that when you have a fish or a shrimp in front of the pump right when it decides to turn on and run backwards. Guess what happens? Your poor animal gets sucked into the pump and then gets minced immediately, killing your expensive, precious pet and also polluting your tank. If you were at work or school, and were not around to do a water change or clean up the mess, guess what? Your whole tank crashes!!! Ask me how I know. Thank you, Hydor! Never again!