I'm trying to get a grip on this heretofore never heard of, before (in my newbie world), thing called gallons per hour. I understand RPM, and know that I get very nervous when my rpms approach 4k. But, I'm an old lady who has always driven a manual transmission! I have good filtration in the 75 gallon now, I hope. But, not too long ago, I heard about these things called powerheads and how much the fish liked them. So, I bought a Hydor 1050-1150 and goodness me, the Harlequin Rasboras and even female bettas were taking joyous risks, diving into the stream! So, I bought another one for the other end of the tank. Sometimes, I run both, but is that a good thing? Sometimes, just one. Sometimes, I change the direction of the flow. Am I overdoing it? And, do powerheads improve filtration, or make it worse?