The bottom vinyl of my cover is sagging and looks like it has blisters. What is wrong?
Unfortunately, these are symptoms of improper water chemistry. You will need a new cover, as there is no way to repair the vinyl. Check with your Dealer as to whether your foam cores are still in good condition, in which case you may be able to replace just the vinyl encasement. Other signs of improper chemical balance can be a drastic color change on the bottom vinyl, the vinyl looks like burlap, or it tears apart easily and falls into the water. It is critical that you get your water chemistry in balance, both for your own health, and the health of your spa. Talk to your local Hot Spring Dealer.
