As part of a recent 80 tank craiglist purchase I received two Aquaclear 420 Powerheads, now renamed AC 50 powerhead. Anyway I have been experimenting using them to see if they increase dissolved O2 which they do substantially to my surprise. However I just wanted to warn that this model is very powerful and if the intake strainer is not protected by a larger intake strainer tube, this powerhead will kill fish up to 2 inches as I unhappily discovered when 2 of my fish each a full 1.5 inches where pulled up into the intake and slammed against the built-in strainer. I discovered them when I noticed the bubbles had stopped and flow had decreased substantially but not all the way. When I shut the power off to investigate, two dead fish came falling out of the powerhead intake bent in a U-shape. As seen in the photo below I have since attached an Aquaclear HOB strainer and haven’t had NO recurrence. So remember the internal strainer provided with these powerful Powerheads is not enough, you need some sort of additional strainer to keep even medium fish from getting sucked in.