CYA not coming up

[TroubleFreePat]

My CYA was getting a bit low (Seems that's the only chemical I add from year to year.) Everything else really stays in check.

So I was around 50PPM. Based on my pool size, I added 34oz by weight of CYA (I bought this CYA the first summer I had the pool, so it's now three years old - could it just be old and losing its strength?)

I add the CYA by slow pouring it down the skimmer. I've tried the socks, pantyhose, etc. Never seems to work well for me. So I always FIRST clean my cartridge filter, then pour it SLOWLY down the skimmer, then check it a week later (And do NOT clean the filter between.)

After a week, I went from 50-60ppm. Huh? It DEFINITELY lowered my pH as I was at 7.5 and by the end of the week I was down to 7.2.

Any thoughts?

At the time I added the CYA, these were my readings -

FC 8
CC <0.5
pH 7.5
TA 80
CH 200
CYA 50

 

[JohnT]

The inaccuracies of the CYA test could easily result in a 20ppm error in your CYA change. That's why we usually recommend you add part of what you think you need and then retest after a week.

 

[TroubleFreePat]

The inaccuracies of the CYA test could easily result in a 20ppm error in your CYA change. That's why we usually recommend you add part of what you think you need and then retest after a week.

Really? A 20ppm error? Wow! Also wonder if it's an issue because I have REALLY good eyes and can really see that dot in the Taylor test!

Anyway, I've tested twice; once a week after adding, and now another week later. Both times 50ppm. Are you saying the error is because we're simply eyeing it up or. . .? Last year I was 70-80 no problem.

 

[TroubleFreePat]

Also, quick follow-up - should I assume the 50PPM I've gotten now is somewhat accurate and I should plan to add more CYA?

 

[JohnT]

Really? A 20ppm error? Wow! Also wonder if it's an issue because I have REALLY good eyes and can really see that dot in the Taylor test!

Anyway, I've tested twice; once a week after adding, and now another week later. Both times 50ppm. Are you saying the error is because we're simply eyeing it up or. . .? Last year I was 70-80 no problem.

At best the test is plus or minus 10ppm. I don't know if it's that good on the low end. If you think your reading is good, I'd go for another 10ppm and see where it goes.