My new plaster pool is COVERED in green stain..

[hausfrau]

Waterbear & sunofthebeach. Thanks for your posts. I should clarify. What killed the algea in the spa was not the acid but a shock to the spa. I isolated the spa from the pool and elevated the Cl enough to kill it then lowered the PH level to 6.5 for 4 hours. Not sure but I believe that the lower PH and short time period should not have attacked the plaster agressively. After the soak I purged the Spa. The spa feeds the pool. (500 gal into 14400 gal). I did not drain from the spa only from the pool so 6.5 PH water never touched the heater. Test strip shows Ca at normal levels for our water after 16 hours of circulation. Testing for Cu in both pool and supply show very low levels.

After the stain removal step. I circulated the pump for three days and the algea returned leading me to believe that a high sustained Cl level is needed to truly rid the pool of algea. As for the staining more than likely we will see what happens after a week or so. I purchased a test kit to get a better testing capability than the strips.

per an earlier post i read a sustained level of 25ppm is needed for shock levels. Any ideas on time period?

[aylad]

Maintain shock levels until the pool clears, the CC goes to less than 0.5, and you're not losing any chlorine when comparing test results from testing at sundown and again in the morning before sun hits the pool.

Janet