After years of being afraid to have too much flow in my tanks, I'm of the opinion now that it's almost impossible to have too much. The more circulation the better, the benefits are too numerous to list. I have 2 Eheim 2217s on a 46 gallon tank, and they keep the water churning pretty well, enough so that you can visibly see the current. Now that I think about it, I think that's a perfect measurement, if you can SEE current from corner to corner in your tank, that's enough flow. If you can SEE debris settling in your tank, that's a bad thing. Don't worry about your fish getting tired or anything, they'll find spots where they can rest.