Nobody touched on this yet,
The problem with reusing the stick on heating pads is not that you might not get them to stick again, it creates a potential safety hazard. When you peel them off of the aquarium, you'll be bending the pad in such a way that you can crack/break the heating element that is encased inside the plastic covering. Either it won't break and nothing will happen, or you could break it cleanly in which case it just won't heat anymore or you could crack it and create a short in the element which could eventually overheat and start a fire. Since it's encased in plastic you can't tell by looking at it whether or not its broken. This is why I don't use the stick on heating pads anymore. Once you stick them on something they're not designed to come off again.3- Can I just peel off the 10-20g UTH off of my 20g tank or would I need to do something to peel it off?