Once you try the polishes out you'll get a quick idea when you need to change. There isn't a set amount on panels that you have to change pads, it all depends. If the pad gets overly saturated with product, you'll need to change it out. It is a good idea to brush off the pad or wipe the pad after every panel or 2 to reduce the build up. You could use a special foam conditioning brish, a nail brush, or a stiff bristled tooth brush. I wipe my pads clean some times with a terry cloth towel to remove excess product. There's a good chance that you will need to use all 4 pads though.