for a 20 that should be great. If I recall correctly that pump puts out about 300gph @ 4ft of head. If it is too much you can throttle it back on the output side but with the all the different fittings you will likely have you shouldn't have to throttle it back at all. That pump is available in your local Petsmart for $49.95 in the pond section under the Pondmaster name.
I have this exact pump on my 55g which is around 6' above the sump... it works fantastic.
Like was said previously, you'll probably be throttling that pump back in a 20... it's just about perfect on my 55.
You're getting a good deal... I paid $99 for my Mag5 at the local LFS (rip-off artists), but I didn't have much choice at the time since I needed it immediately.
I think 300GPH is about the same flow that comes out of your faucet, so you can see how much water it will pump.
My Mag5 has been going 24/7 since I got it and I haven't even had to clean it yet (going on 5 months).
They're great little pumps.
cool, thanks for the info, if anyone is still lookin for pumps Petsolutions is having a sale on mag drives,, right now you can get a mag 7 for $45.00 if ordered over the internet, great deals.
Check it out at www.persolutions.com