I let my pads soak in HOT water with APC in a bucket.
Repeat above method one more time. When water is warm enough to work the pads with your hands in the bucket , massage all residues out.
Rinse clean and squeeze dry. If there's built up residue that you cannot work out by hand embedded in the pad. Repeat process except have a pad cleaning tool, clean the pads in the bucket using the buckets edge for backing. Give it a few good rolls under water in a 50/50 mix Water:Apc.
If the pads, or any pad/applicator / foam tool that is not properly cleaned after use becomes hard.
This is especially true if pad,applicator etc have sat without proper cleaning for an extended period of time or they see a lot of shelf life. In my experience it will never clean back to new again! And most the time I toss them when they get to this stage.
Sorry for the story lol. Another good use for certain applicators for wax and dressings you can use as a tire dressing applicator and cut it in half or use whole so you can get mutli purpose use before tossing.
Just my .02