Using an old saltwater tank for a freshwater setup

[TheDude]

Hey all, recently I found a jbj 20 gal rimless cube. I've only ever done freshwater tanks and haven't used a setup like this before.

Main questions are, how does the build in filtration work and will it work for a freshwater tank?

Found this on offer up, love the look of this tank. I don't see any issues using it as a freshwater tank, but just want to be sure. Any help or advice would be greatly appreciated

[BigRedsReefs10]

You just put your media/sponge in the first chamber, I run my heater in the second chamber and nothing with the return pump. You can look into buying or making a media rack for the first chamber to make maintenance easier.