Hi I have a 900 gallon in-ground gunite spa attached to my pool. The pool is closed for the winter but the spa is open and I have used it several times this winter. This is a saltwater pool/spa with a pentair salt cell generator that works during the summer. The salt level in the spa has been low so on days I want to use the spa I put on the heater, add a bit of sanitizer and maybe a little muriatic acid to knock down the ph and the water has been great. A couple of weeks ago I decided to add salt to get it over 3400 so the salt generator could start working. I had to add a lot of salt but got it to 3600 and had all green lights on the generator and I just left it. Keep in mind the spa is not heated so he average temp has been about 55F. Yesterday I tested the water- Yikes!!! My ph test turned purple and chlorine test powder made pink clumps before turning clear. I could not get any readings so went to my local pool store. Their test showed F Ch=.13, T Ch=15, ph=8.5, T Alk=0 (yes 0). They told me first step I need to raise the T Alk by adding 1lb 5oz of baking soda, which I did- nothing. So I added another pound, and another, but still could not raise the T Alk!?!? Today I went back to the store and found the only thing that changed was the F Ch=15. The T Alk was still 0. Again they told me to add 1lb 5oz of baking soda and get the alkalinity up. I said it does not work and they said you have to add it slowly- only 15oz at a time with 4 hours in between. It does not really make sense to me how quickly you add it but this is what I am doing. Am I getting bad advice? Any suggestions? Thanks for your time.