Nice Tank.
I'm in Beavercreek and i have a 15 gallon tank with a sponge filter (we could pull a sponge from my display to seed it) + hang on back filter + heater/lid I'm not using-- you could borrow it you decide to pull them. I could live without it for 90 days.
Also, I think Petco has their $/gallon sale for a couple more days (until January 28th)... you could put together a QT/Med tank pretty cheap.
You might find your new fish got the ich form the tank (and your current residents are immune at low levels), so it might self resolve. if it's Ich you might see it again in about 3 days.
Does your spotted fish have any dark spots, and does it look dusty or more like salt, hiding from light, swimming in place facing a powerhead? Just watch for these signs of velvet.