I've kept lots of pretty delicate fish. I don't use Purigen for FW
tanks (no ill effects) but you can if you want to. I'd probably substitute ceramic media for bio balls- brand name does not matter. All the biological media does is provide surface area for your bacteria to colonize. It's 6 of one half dozen of the other. Many models of canister filters will come with sponge pads or similar. Use the coarse sponge where the incoming water first contacts it (in my Rena Filstars, that is on the bottom), then use your finer pad(s), then your bio media, then your floss/polishing pad/whatever if you choose to use one.
Ultimately, there are a lot of different ways to do it and products to use, and the end result is pretty much the same.