Get a better heater, a "good" Aqueon heater costs $20 or less on Amazon. A cheap heater will have large swings (I bought a cheap one once, and it had 8 degree swings. The Aqueon is maybe 1.5 degrees. Also size it correctly, bigger isn't always better.
I keep a bag of ceramic media (biomax) in my sump in the DT. When I need to QT, I pull some of the ceramic out and put it in the HOB. I then replenish the missing media in the sump.
I never reuse the media, it is pretty cheap.
Yeah I ended up ordering an eheim one last one, I didn't want to risk it as it's actually been a little chilly in socal lately.
I have the marinepure balls and I have some seachem matrix I could snatch some of that too I guess.