I'm thinking of setting up a 20g long to be a low tech, planted tank. And 80% of the time, there wouldn't be anyone in there. But if I made a new fish purchase, or someone needed to recover, then I'd have a place they could go. I hadn't been using a tank like that before, but after battling ick, I'm now a believer.
Although it's a short duration stay in the tank, I'm guessing that I would need some type of filter, right? Would it need to be a 20g filter though since it would always be very understocked? Earlier this year I had gotten a Zoo Med 501 for my daughter's 10g tank and I've been happy with it. Cheap, effective, and quiet.
Also, if there's no one in the tank, would I need to do water changes? Or is topping it off acceptable?