Hide and seek CYA

[frbruno64]

Although there are plenty of informative posts about unexpected CYA levels upon opening, I post mine because of unexpected results based upon the quantity and types of chemicals added over the past month.

The pool was closed early September 2015.

• Balanced with a CYA value of 60
• Water lowered under skimmer
• Protected with a solid cover

One week before Memorial Day 2016, with city water added to mid-skimmer, I was surprised with an initial CYA value of zero. I admit to being uncertain if I tested before or after starting the pump. Although my reagent was within date, I was perplexed enough to seek a second opinion. I am absolutely certain that the pump was running for several days before I pulled a sample for testing by my local, independent pool store. Their test, just before Memorial Day, also showed CYA to be zero.

Since then, the following actions have been taken.

• Over the first three weeks, regular additions of liquid and granular kept the pool sparkling with a consistent chlorine level of 3-5.
• During this time, I utilized 10 gallons of liquid 12% and 15 lbs. of Dichlor-S-Trianzinetrione.
• While my expectation was that CYA was slowly increasing, it appeared to barely budge based upon my kit, and supported the apparent chlorine demand.
• Last week, the cloudy green hue of trouble appeared.
• Out of liquid and unable to resupply due to ankle surgery, I added 4 lbs. of dry stabilizer via skimmer sock and broadcasted my final 10 lbs. of granular Dichlor.
• Today, CYA is suddenly reading 80 at the pool store and over 100 by dilution test with my kit using new reagent.
• Chlorine is near 15 by my distilled water dilution test.
• Green is the color of the day, although with reduced cloudiness.

Based upon the calculator,

• 4lbs of dry stabilizer (64 dry ounces) should result in a CYA increase of 15 for my 33k gallons.
• Adding 25 lbs. of Dichlor (400 dry ounces) should have resulted in a CYA increase of 46 for 33k gallons.
• Total CYA should have increased to 61, assuming zero start, (higher than desired but I panicked)
• Yet it reads at least 80 by one test and over 100 by another.

I’m beginning to suspect that the opening CYA value of zero was incorrect and that a healthy amount was hiding with the intention of messing with my sanity.

Thoughts and questions from the group are greatly appreciated. Thank you.


TC 15
CH 280
TA 110
pH 7.8
CYA unreliable results to date
Temp 80

 

[UN1017]

I think you are spot on with your assessment. I'd put money on you were at least 20-30 from the start. I know we want to have faith in our local pool stores but unfortunately they are prone to the same errors as the national chains. We don't know their testing methods either. Your situation really shows the trouble people get themselves into if they rely solely on the pool store's recommendations.

You are here now...and you have your own test kit. This should never happen to you again.

On a side note, to really be properly equipped you should add the FAS-DPD test to your existing kit as well.

 

[MarianParoo]

The 1005 is also missing the TA test. Can you swing for a new testkit? Pool School - Test Kits Compared

Your CYA is over 100 with dilution with the 1005? Can you drain and refill?

 

[frbruno64]

Thanks for the input. My 1005 kit is several years old and includes an alkalinity test. I replace reagents as needed, but that is getting old. As UN1017 mentioned above, I need to get the FAS-DPD test - and FAST! So, your advice to purchase a new kit is on the money.

Note that whenever I mention a dilution test, the value I present is the total result after appropriate multiplication. Thus my CYA dilution test produced an initial result of 50. The final result requires multiplying by 2 to obtain the final value of 100.

Yes, I can easily drain a good portion of the water and refill - obviously for a one-time price.