I have a 100-gallon rated Cascade HOB on my 29 gallon. Keeps a nice current going. I love it, because it keeps my betta active, and if you ask me, they are boring fish if left in a bowl. I like the current keeping my fish active, and they can always hide in the conch or their ornament to get away from it.
Shame one of my two new silver dollars wasn't strong enough to avoid the intake; three times he got caught. The sad part was, my painted tetras are the same size and have no problems. At least the other silver was fine. I suspect that the one that got sucked in was sick, stressed, or just weak. It happens I suppose.
Although it is sad to see a LIVE fish get stuck to the intake.