Originally Posted by Roemgie
I personally would like the 10 gallon to have a sponge filter instead. How would I do that without having to start all over again?
When you get the new sponge filter, wet it in tank water and then squeeze the filter cartridge from the cycled hang-on-back filter all over the sponge - then install the sponge and use it as you normally would. This will seed the sponge, but it will take time for the bacteria to breed and fully establish.
0-0.25 ammonia is normal, especially in a newer tank that is getting the cycle established. Nitrites look good and nitrates indicate that bacteria is present and working.
You'll want to keep your nitrates at 40ppm or less. You accomplish that with a large water change.
Honestly, it looks like it's ready for a fish if you leave the HOB filter installed. If you switch to a sponge, I'd give it another couple of weeks, unless you want to do a fish-in cycle (my normal course of action) which means you'll need more frequent testing and water changes for a while.