I'm setting up a 20 gallon tall high tech tank that will be heavily planted, and am looking for a good filter. I'd like to use the eheim classic series, and found a good deal on a 2217 and a 2213. From what I've read on here, the 2213 seems like it will be a bit under-powered. Is this correct? is the 2217 too much for a 20 gallon? thanks for the help!