I have noticed over the last three years that our "elevated over flow waterfall spa" surface on both seats and vertical walls is very pitted when we pull the cover off in Spring. The rest of the pool is still covered, but I did open the Spa yesterday by peeling the spa cover back and pulling the return plugs in the spa. The pool is usually smooth, it's only the spa....When spa water was tested this week, I saw the pH was off the charts, deep purple....the FC was 0, and the TA was about 40, CYA around 20. Calcium was pegged at 400. Before use I have added acid and CL, and have it around 7.2 and 3.0 ppm now. When we went in the Spa for the first time yesterday, it was worse than sitting on 20 grid sandpaper. Mama wasn't too happy. This is at least the third year of this situation...so I thought I'd reach out to the Forum. Last two years I used a Lava stone to flatten out the rough peaks. So, I am asking: is there something I should do before closing each year. I certainly carefully balance the pool and spa per TFP recommendations before closing, and just for the heck of it usually take the FC up to about 20 ppm using 73% Cal-Hypo the day the cover goes on, before shutting off the pump, letting it run a few hours, and later doing all the closing steps required. Would it be a good idea to drain the spa and perform an acid wash? It would worry me to do the each and every year. If yes, should I use 25% liquid acid/water, or perhaps 50% liquid acid/water (using the 31 BAUM muriatic acid).? Should I periodically add "heavily diluted" acid in to the spa during the winter? Puzzled. Thanks!