Well I bought an eheim 2217 because I am so used to buying much larger filters than I need from keeping SW and cichlids. I now realize 264 in a 25cube is a little insane. I have lily pipes. I haven't filled my tank yet; however, I wanted to know if throttling down the flow with one side of the output double tap will really cause back pressure on these filters. I see numerous posts on different forums where people swear by this method of reducing flow. Would it also benefit replacing it with a 2215 impeller? I am running an inline heater and diffuser...but nothing to really obstruct flow. I seem to worry more about the actual force created by the canister than the actual flow. If I do throttle the output do I just use one side of the output or both levers(canister side of the double tap or output line side of the double tap)?