Well, might as well reply to this one since it's been a while from when you posted. . . . I also maintain a 20g long planted, and I can imagine a canister filter being a bit too much for it. I currently operate a penguin (not ideal, I know) and a powerhead at the opposite end, which gives a nice amount of circulation.
I have been in the habit lately of turning off the power filter when feeding. This way I lose less food to the substrate. . .