Using a sump tank during transition from FW/brackish to salt

[Meatloaf]

I'm in the planning stages of my first puffer tank, also using my first sump tank as well. Planning on 2 GSPs. I have a 65g tank, and a 20g long tank for the sump. The 65 g tank is empty currently, but I'd like to set up the plumbing and everything for the sump before I do anything.

What can I put in the sump to help filtration while the water is still fresh/brackish? Pot scrubbies? When it comes to full marine, do I leave them in when I replace them with live rock? Would it be possible to use the sump as the only filtration when it's fresh?
Thanks for the help

[SammyDee]

You can use the bio balls for SW and FW. Some do choose to remove it after a while for live rock. I use bio balls in my reef tank sump with no issues thou. I have GSP too love these guys lol

[Mezzovex]

in my 125g fahaka tank. I have a built in skimmer box, which is full of bio balls. then i have a wet\dry trickle filter (filled with layers of bio balls and quilt batting) that then dropps into my 30g sump. where it sits with some java moss, then it gets sucked out by a external pump, pushed through a canister filter (totally not needed) and back up to the tank