CYA too high

[KarenT]

(using Taylor K2006 kit)

Two weeks ago I went on vacation and put one puck in the skimmer while I was gone. I'd had some algae problems earlier this summer and didn't want to risk more while I was gone. The pool was left up over the winter, drained partly, and I added lots of bleach after refilling when we opened in May, but no CYA. I believe I was previously reading the CYA level incorrectly b/c I had always written down <100 and now I realize the scale reads from bottom to top, duh.

We have had a ton of rain this summer so I am surprised the CYA is still so high. I had not been able to test it for awhile b/c the test kit ran out of the reagent and I had to order more. A few days ago the pool was starting to look green and I didn't have time to test it (working full time long hours) so I added a half gallon of bleach. I was planning to add borates to help combat the algae so tested everything today (refills arrived in mail)

pH 8.0
FC 5.5 ppm
CC 0.5 ppm
TA 90 ppm
CYA >100 (diluted 50/50 with tap water - 80, so really 160)
CH 100 ppm

I was all set to add muriatic acid since I'd bought it in preparation for the borates anyway, only to realize I need to do something about the CYA first.
I have a science background but chemistry was my weakest part - if CYA is acid, why is my pH so high?
Is one puck in a ~5000 gal pool really that bad, or perhaps it's been too high all along and I didn't realize it from reading the scale wrong. Is draining my only choice now?

Is the water dangerous to swim in with the CYA that high?

 

[chem geek]

The pH doesn't change because of a static amount of chemical in the pool. That is, having CYA already in the pool will not lower the pH. If you were to add CYA to the pool then the pH would drop some, but only some because CYA is a weak acid unlike Muriatic Acid that is a strong acid.

One 3" 8-ounce Trichlor puck in 5000 gallons will raise the FC by 11 ppm and the CYA by 6.7 ppm. Your CYA is very high because you were misreading the CYA test, though even this one puck didn't help.

Your pH may have risen from carbon dioxide outgassing and it's possible that the raindrops contributed to that by splashing the water aerating it which increases the rate of gas exchange between the water and the air.

As for as danger for your water, it depends on your actual CYA level and the FC level. If we assume your CYA is something like 150 ppm, then having your FC at around 11 ppm should be fine. However, we don't know your true CYA level. Order some more reagent and test, diluting 1:1 with tap water and then double the CYA reading to get the true level (assuming it's between 100 and 200; if it's more, then dilute at a higher rate). Then do partial drain/refill of your pool water to get your CYA level lower.

 

[KarenT]

You missed in my notes - I did dilute it 50/50 and then I got 80, so I'm assuming the real CYA is 160.
Thanks for your info - I guess I will be draining tomorrow. First have to get the grass around it mowed, since it's rained all week and only just now dried enough for that.