I have a 4 year old, 20,000 gal, gunite pool with dark gray plaster. When the pool was plastered the company told me to keep the pH on the higher end to prevent etching of the plaster which could affect the color. I am diligent in keeping my water in balance and have maintained the pool at a pH of 7.6 and a TA of 100-110. A couple of years ago I started noticing white spots and mottling. Thinking this was something leaching out of the plaster I kept the pH high. The embarrassing part is I never really paid attention to my CH. I am on well water and the CH out of the tap is 350-400. After 4 years of evaporation the pool has a CH of 800!! About 80 % of the pool is now covered in Calcium Scale, which I finally read up on and realized the mistake I made. About a month ago I lowered the pH to 7.0-7.2 with a TA of 70-80. I have already noticed some lessening of the scale and I have vigorously scrubbed some test spots with a brush and pool stone and that has worked but not practical for the entire pool.
I now realize I need to do an acid wash, but being in So Cal I want to avoid draining the pool. I have done some reading about No-Drain Acid Baths (Zero Alkalinity Treatment) on this site as well as others but I am finding conflicting information. My questions are:
Once the scale is gone I will have a company come in and do a reverse osmosis treatment to prevent this issue in the future.
current test results:
pH - 7.0 / TA - 80 / FC - 4 / CH - >800 / CYA - 0 / Borate 20 / CSI -0.36 (I realize my CYA and Borate are deficient but I don't want to bring them up until I have the water treatment.)
I use liquid chlorine, muriatic acid, baking soda, borate as chemicals
I now realize I need to do an acid wash, but being in So Cal I want to avoid draining the pool. I have done some reading about No-Drain Acid Baths (Zero Alkalinity Treatment) on this site as well as others but I am finding conflicting information. My questions are:
- Some sites recommend adding 4 gals of acid per 20,000 gals,others say add 10-12 gals. So is it better to use the lower acid amounts and treat for a longer period of time or use higher acid amounts for a shorter amount of time?
- Should I monitor the pH level or is keeping the pool at zero TA all I need to worry about? If I need to monitor the pH, how do I do this as the tests only go to 6. (I use a Taylor test kit.)
- Has anyone actually used this method with success?
- Once the scale is removed does it stay in solution or is it suspended and then can be filtered out.
Once the scale is gone I will have a company come in and do a reverse osmosis treatment to prevent this issue in the future.
current test results:
pH - 7.0 / TA - 80 / FC - 4 / CH - >800 / CYA - 0 / Borate 20 / CSI -0.36 (I realize my CYA and Borate are deficient but I don't want to bring them up until I have the water treatment.)
I use liquid chlorine, muriatic acid, baking soda, borate as chemicals
Here at TFP we also refer to the no drain acid wash as the Zero Alkalinity Treatment as see here: 
