Hi all,
I don't think you can use a different impeller on the 2213, it is on the 2215 that you can put the impeller from the 2217 in to improve flow speed. I've tried this, but it doesn't work on the 2213, as the 2217 impeller is physically too large to fit.
You could try different media, I think the internal sponges tend to reduce flow rate, I run the 2213 with just a PPI10 sponge pre-filter on the intake and the central container 3/4 full of ceramic rings.
Another option is to make sure you don't have any excess hose, and that the hose you do have isn't constricted or kinked. The shorter, straighter and cleaner the hoses are the smaller effect they will have on flow speed. If you can do without the spray bar that will also help.
cheers Darrel