Water Polishing

[elmo666]

Hi everyone. Any suggestions on what to put in a second external on a 300ltr set up. Its an eheim 2224, came with no media but wasn't worried as I only want to use it for fine water polishing. I've initially cut a large fine white matting to shape, but would like to improve on this if possible. My other filter is an eheim pro 3 full of biological media. Could I now take the fine filter pad out of this to make room for some siporax or similar? Thanks