The only way you're going to get rid of the stress coat is skim it away. Even large water changes won't remove it, just dilutes it. Everyone has given you good hints so far to reduce the overflowing enough so that the slimy foam spilling over into your collection cup is the removal of the stress coat. Just pour out whatever you get daily, DO NOT pour it back into the sump for any reason thinking it is just water, because it isn't, or that will just make things worst. Replenish your lost water with freshly made saltwater. After awhile, the skimmer will stop going nuts and you can readjust the air back up and then your exhaust as well. It will take daily removal for at least a week. Good luck!