CYA Question

[wler711]

Hello,

I have a question concerning the CYA level of my pool. I'm a relatively new pool owner but have done extensive research here and at poolcalculator.com. I bought a house about a month ago with a dark green, very swampy 20k gallon inground pool. Based solely on the information I learned here and on the Pool Calculator (and a little common sense), I had the water in my pool crystal clear and, had the temperature been a little warmer, ready for swimming in a little less than 2 weeks. That's how awesome you guys are!

But, I digress. According to the Pool Calculator, the only practical way of reducing CYA levels is to replace water. That leads me to believe that once you reach a certain CYA level, you shouldn't need to add any more CYA under normal circumstances. In other words, the CYA level shouldn't naturally drift like FC or pH does, correct? However, when I recently went to my local pool supply store to buy some CYA, a salesman tried to sell me some trichlor tabs. Armed with the knowledge that trichlor also adds CYA, I told him that I would rather not be constantly adding CYA. He then told me that unless I used trichlor tabs, I would always need to keep adding CYA and that it was one of the most expensive pool chemicals (he was definitely correct on that front). I pretty much dismissed him, bought a 7 lb bag of CYA, and went about adding it to my pool. I realize that CYA is very slow to dissolve, so I put about a pound or two in a sock, tied it off, put it in my skimmer for about a week until it was all dissolved, then repeated the process. Here is my issue: When I first started this process, my CYA level climbed to about 50 ppm after the first couple of times of adding CYA. However, I've added CYA about 5 times since then, and I can't seem to get my CYA level above 50 ppm. My pool is unscreened and gets a full day of direct, Florida sun, so ideally I would like my CYA level at about 75 ppm.

Any idea what I might be doing wrong? Was the guy at the pool store correct in saying that unless I use trichlor or dichlor, I would indeed need to constantly add CYA? Any words of wisdom you can offer would be much appreciated!

 

[JohnT]

Welcome to the forum.

When the pool is maintained with circulation and chlorine, CYA only goes down if you remove water from the pool (splashout, backwashing, draining or a leak) and then replace it with fresh water. Evaporation doesn't affect it. So you normally don't see much of a change during a swimming season unless you are using stabilized chlorine. I raise mine in the spring and usually check it about the first of August, but usually don't need to add any then.

How are you testing your CYA level? The CYA test is far and away the most difficult test to perform accurately, and +/-20ppm is probably what most people get with the turbidity test.

Trichlor is fine as long as you keep an eye on your CYA level. It's easy to use, and probably more likely to be on sale than CYA alone.

 

[wler711]

Thanks for the response.

That's what I suspected with regard to the permanence of CYA levels. Yes, I am using the turbidity test to determine my CYA level (I use the Taylor K-2006 kit). And I agree, it is pretty difficult (and frustrating) to determine the exact level at which to take the reading. I often think that I reach the point where I can no longer see the dot while I'm adding the test sample, and then when I look at it again just a few seconds later after reading the tube, it seems that I can see the dot again. It's unfortunate that there isn't a more objective way of measuring it. But if +/- 20 ppm is the norm for testing CYA, I guess I'll assume that I've reached my desired level and leave it at that.

Thanks again for the information!

 

[duraleigh]

wler,

Welcome to the forum. Your knowledge is correct and the pool store guy is incorrect. CYA, once added, stays in your pool. I can think of three possibilities for your inability to lift CYA over 50ppm.....

1. Testing error - tell us how you are testing, as JohnT indicated.

2. Splashout - If you have a ton of kids that are splashing out 2-6 inches of water daily, you will, in a week or so, have re-supplied your pool with water that has no CYA.

3. Auto-fill - similar to #2, if you have an undetected leak and have an auto-fill feature, you will be re-filling with fresh water that has no CYA.

I would suspect testing error first, but the others are possibilities.

 

[Bama Rambler]

Adding 7lbs of 100% cyanuric acid will have raise your CYA by 42 in a 20,000 gallon pool.

Can you post a full set of test results for us?

pH
FC
CC
TA
CH
CYA

 

[orthofish]

Are you using 100% CYA??? I made the mistake of buying stabilizer that was only 50% CYA Only once :-D

 

[PaulR]

Regarding the CYA test, two things. First, bright indirect light is best; Taylor recommends outdoors with your back to the sun. Second, you can run the black-dot part of the test several times with the same sample, to be sure you are consistent about reading the point where the black dot has just disappeared.
--paulr

 

[TimS]

A couple of issues I've noticed with the CYA test:

1. I was relying on memory for how to perform the test, (and that memory was from a cheapie test, not the TF-100.) I was failing to get the water to room temperature, and not mixing and waiting long enough. Easily fixed, once I read the directions again.

2. As I'm filling the tube, the dispenser bottle creates a lot of bubbles in the tube. If I wait a few seconds after the dot disappears, it will usually show up again. I fill again, wait again, etc. Eventually it will disappear and not reappear. I'm still working on getting the sample into the tube without creating those bubbles. I know I simply have to do it more slowly, but I'm still not slow enough.

Running the test multiple times with the same sample will allow me to average my results, and I'll be fairly confident of my reading +/-5ppm or so.

 

[PaulR]

With the TF100 mixing bottle you can squirt down the side of the view tube, makes for very few bubbles.
--paulr

 

[TimS]

With the TF100 mixing bottle you can squirt down the side of the view tube, makes for very few bubbles.
--paulr

Yes, that does help, but I still get quite a few. I know this is simply me squeezing it out too fast. When I slow it down, it helps a lot. I've even considered making the hole in the tip of the bottle a bit bigger so that it will pour faster at lower pressure. I have a bad habit of getting in a hurry with this particular test.

I also will sometimes use the tube and mixing bottle that came with another kit, since the mixing bottle pours faster. The biggest problem with this is that it's about 1/2 the size of the one that comes with the TF-100, and thus is harder to read while pouring solution. That makes it easy to overshoot.

It's too bad that all of the tests can't be like the FAS-DPD - simply count drops until the solution goes clear and you're done. No color matching, no disappearing dots, no watching to see if the color stops changing.