Testing CYA

Terry Brewer

Member
Jul 27, 2010
21
Ashland, KY
Whats the best way to test CYA. I have theTF100 test kit. Hold the test tube at waist level until you see the dot disappear. (Completely). Looks like the test could vary at least 10. Is there a better way to test CYA? What would be a good level to have cya? Right now I'm thinking mine is 50 - 60. Why can you swim when Cya 50 and FC is 5 but when cya is 0 and FC is 4 thats to much?
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
20,396
San Dimas, CA (LA County)
Sounds like you have it figured. The test is subjective, but it's the only one we have. Most of us take our reading, pour the sample back into the mixing bottle, shake it some more, then try again a few times. If I get the same number 3X, that's what I call it.

The chlorine is sort of bound to the CYA molecules, which is why it's not dangerous. Only a portion of the chlorine is "loose". In unstabilized water, all of it is "loose." If you remember chemistry from school, think of a buffered solution. Also remember that cyanide is deadly, but when it's combined to make cyanuric acid, it's not. Chlorine by itself is a toxic gas; combined with sodium it's just plain old salt, which we need to survive!
 

flintstone

LifeTime Supporter
Jul 17, 2007
99
Rockville, CA
The test for CYA is likely the second most difficult test to complete and interpret accurately, right behind the CH test. You should read the results of the test when standing outside with the sun at your back. I have found the ability to see whether the dot has disappeared is much easier to do this way.
 

Ohm_Boy

TFP Expert
May 1, 2007
1,344
Orlando, FL
The important aspect is consistency. The potential for interpretation on the CYA test is one of the best arguments for doing your own testing. You will develop a routine which will be repeatable for you. Plus or minus 10 will not make a killer difference in your levels, as long as the result is consistent. Over time, with repeatable test methods, you will dial in your FC level to suit your pool, and it will be easy to maintain that.
Pool store testing can have HUGE variance in method and interpretation, and is tough to hang your hat on from one reading to the next. Strips are worse.
 

Terry Brewer

Member
Jul 27, 2010
21
Ashland, KY
Thanks for the info. I was thinking my cya number was to high,50. But after reviewing this sight I believe I'm right on target. I was also worried about caring a high chlorine level 5, The pool stores say they would never swim in water that high. They do not know that cya binds the chlorine and you need a higher chlorine level to sanitize you pool.
 

tim_pool_newbie

Bronze Supporter
LifeTime Supporter
Oct 6, 2009
161
I too have difficulty with the CYA test, and my results always vary within 10 points of each other. In fact, my CYA is between 50-60 right now as well (I'm leaning more towards 60).

I recently brought a water sample to the pool store, and they told me my CYA level was 30!!! Now that's a big difference!!!

Thanks Richard for the idea of pouring the solution back into the bottle and repeating the test till we get the same number 3X. I'm gonna try that!
 

frustratedpoolmom

TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
12,177
SWSuburban Chicago, IL
Make sure you do it outdoors in sunlight, with your back to the sun to shield the view tube with your body.

If pool stores are doing the test indoors, that could explain some differences. Some pool stores also use computer-read strips, which are horrible for detecting CYA accurately.
 

Bama Rambler

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2009
22,958
SouthWest Alabama
The CYA test is one of the most inaccurate tests that the Pool Store performs. On more than one occasion I've had them tell me there was CYA in tap water and not just a little either. I've also had them tell me it was over 100 when I haven't used a drop of stabilized chlorine in over two years.

I said that to say this, trust your own testing!
 

Ohm_Boy

TFP Expert
May 1, 2007
1,344
Orlando, FL
We've heard many anecdotes about pool store testing, ranging from taking the same water to different stores to see how their results compare, to using three people and giving the same store three bottles of the same pool water and getting wildly different results. Pool store testing is often only better than no test at all.
 
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