Yup exactly. Thats what most experienced peeps will do - just leave a sponge in the sump so its seeded with bacteria. It will take time for that beneficial bacteria buildup though.I don't, I'm buying my sw from my lfs, but I can do the sponge thing np.
I have the filter media stuff and sponges. Should I bag em and put them in my dt till after the cycle? Then I can just put them in the canister with fresh saltwater and be cycled?
Very important - make sure when you finish the quarantine not just to throw the media bag back into your DT sump! I would discard the media, but if you wanted to reuse it you'll want to completely sterilize it and dry it out before throwing it in your DT sump. If you use any copper or non-reef safe meds, I would not keep it since it can absorb the meds.