High CYA - Need to Drain??

[mdchristopher]

Good afternoon. I just performed a chemical test as I was starting to see some yellow/mustard growth in the corners of my pool. I've been using Chlorox 3" tabs from Costco as well as the Chlorox shock bags from Costco. After reading some threads I'm concerned this has caused my CYA levels to elevate possibly above salvageable without draining the pool. I've ordered and will be picking up this afternoon 8 gallons of 10% liquid chlorine from Wal-Mart.

Approximately 15,500 Gallons
Pentair DE Filter
FC = 2.5
CC = 0.5
TC = 3.0
CH = 500
pH = 7.5
TA = 120
CYA = 120+ The test tube with TF-100 starts at 100. However, I couldn't see the dot before we reached 100 level. I'm guessing around 120+ after using a PoolRx test strip that indicates the CYA to be close to 150.

Please help me understand if I can save the current water, or need to do a partial/full drain in order to bring the CYA levels down. I have muriatic acid, will be picking up liquid chlorine at 10% and 100% sodium bicarbonate.

 

[mknauss]

Welcome to the forum!
No need for the baking soda. Your TA is high now.

Do the extended CYA test. See Step 8 in CYA - Cyanuric Acid Test - Trouble Free Pool

Start to determine how you are going to do a fairly large water exchange. At least 50%, probably more.

I suggest you read ABC's of Pool Water Chemistry.

 

[mdchristopher]

Ok, thanks. Performed the extended CYA and came up with 95 so x2 = 190 for CYA. The pool is only a couple years old and this will be the 2nd drain/3rd fill. The previous was by the builder to fix some staining in the PebbleTec finish. In-ground gunite/pebble finish in Central TX.

Do you have any recommendations on the high calcium hardness?

I've read through the ABC's, but I'm no chemist. It sounds like slightly more work, but the liquid chlorine without the CYA appears to be the path to go. (We have really hard water here, and the pool builder mentioned to watch CYA. The water company chlorinates the water sometimes too much I hear.)

 

[mknauss]

CH is manageable at the level you show. What is the CH of your fill water?

Sadly you need to drain and refill or exchange at least 75% of your pool water volume.

You then need to commit to using liquid chlorine every day to sanitize your pool water or look into installing a SaltWater Chlorine Generator.

The 'chlorine' the city adds to water is not of any issue. In fact, they probably add chloramines, that what smells like 'chlorine', even though it is not that.