CYA seems lower than it should, okay to add more?

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AndyfromTucson

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Jul 22, 2012
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I have a 20,000 gallon pool with SWG that was installed in the spring of 2010. The pool company put 4 lbs of CYA in at that time. A couple months later I tested the CYA myself (Taylor kit) and it was low, so I added another 4 lbs.

Fast forward to this year, I was having trouble with CL dropping faster than it should, so I tested CYA again, and it was too low to make the black dot disappear (my Taylor tube stops at 30 and the dot was still faintly visible). So I added 8 lbs of CYA last weekend. Today I checked the CYA and it was at 40ppm. According to the online Pool Calculator the 8 lbs I added last weekend should have gotten my CYA up to around 48ppm even if I had zero to start with.

So, my question is: Should I go ahead and add another 4 lbs of CYA (which should get me up to around 65ppm)? Or should I stop and check something before adding more CYA. The reason I am unsure what to do is that I have read that CYA is only lowered by replacing water, and my pool has never been drained or had substantial splash out, so I am wondering if somehow the Taylor black dot test is reading way too low and I really have a ton of CYA in the pool already?

By the way, I took a sample to the local pool store last weekend just after I had added 4 lbs CYA and watched the clerk do the CYA test. She got 40ppm using a black dot test, but when I asked her to show me the black dot it was still visible (but blurry) at 40ppm. I moved the dot to where it truly vanished and it read 30ppm.

By the way, the troublefreepool forums have provided me with an excellent education, so I will take the occasion of my first post to say thanks to all the people who have contributed here!
 
There are some reports of the CYA dropping over winter in closed pools.

I would trust your own testing and adding another 4 lbs seems reasonable. Is there a chance the pool holds more water than you think?

How are all your other levels? They converted CYA sometimes shows up as high CC levels.

Posted from my Droid with Tapatalk ... sorry if my response is short ;)
 
Do you get a lot of rain or snow over the winter? All that fresh water could change the values of CYA if it creates any overflow or drainage. In a normal wet winter here in Houston, I see CYA and CH levels are much lower in spring.

I would wait and see if your chlorine is holding better before adding much more CYA. Work with the calculated value, and know that there may have been 30 there to begin with, which puts you near where you want to be. Where are you located? In Texas and Florida, Arizona and such you will want to run up to maybe 85 CYA, less than that in cooler areas.
 
I calculated my volume from scratch and got 21,000 gallons, so I don't think that is the problem.

My CL seems to be holding a lot better. I used to have the SWG (IC-40) at 100% for 8 hours a day and the CL would never get over 1.5. Now with the CYA added it seems to hold at CL = 3 with the SWG at 60% for 8 hours a day.

I am located in Tucson AZ. We have never gotten enough rain to make the pool overflow. I don't cover the pool or do anything else special for the winter.

Adding it up, the pool has had 16 lbs of CYA put in it in the two years since it was built. According to the Pool Calculator I should have CYA of around 90, but my Taylor black dot test says 40. So either (1) there is some mystery mechanism for CYA loss, or (2) the Taylor black dot test is

By the way, my CH is crazy high: 1300. Could that throw off the CYA test, or somehow consume the CYA?
 
I should have realized you did not close the pool based on your name.

The CH will not affect the CYA level.

What stabilizer did you use? We have seen a few reports of weaker stuff ... what % is listed on the container?

Posted from my Droid with Tapatalk ... sorry if my response is short ;)
 
2010: 4 lbs of unknown brand CYA put in by pool company; 4lbs Leslie's
2012: 8 lbs of Kem-Tek.

I don't think it is a problem of faux CYA because:
- Each time CYA was added the CL retention was substantially boosted; and
- The CL retention became really poor in late spring 2012 after being okay in 2011.

I have never backwashed either (cartridge filter). I know of literally no instances where a significant amount of water left the pool (except by evaporation of course).

Speculation: A few times this spring when I was out of town the water balance got way off and the SWG was generating huge amounts of white calcite flakes (or whatever they are), plus it got pretty clogged with deposits. Any possibility that the white flake generation process somehow took CYA out of the water?
 
You added CYA last weekend; I suggest waiting a full 2 weeks before you add any more. Then what is there will certainly show up on test.

Just reaching here, but have you gotten any of those dust storms?
 
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