CYA Test Differences

[gadgetman9]

This is kind of a weird thing. When I test my CYA with my Taylor K-2006 kit I get a high reading of 80. When I bring a sample to the local pool store they get a reading of 25. In the Taylor kit, I add solution until the dot on the bottom of the tube disappears. In the pool store test it has a black dot on a slide in a graduated cylinder which you can vary it's depth in the solution until it just disappears and read the CYA level from a scale on the slide.
The solution in the Taylor kit is the same as the pool store. Both kits mix solution and water for the test media. In the Taylor kit, I mix 7 ml of water and 7 ml of solution for 30 seconds. In the pool kit, I add water to one mark, and solution to the next up and work the slide 5 times.
They even gave me some new solution and their test tube. (for free) to take home and try. Results are still the same difference, even when using the new solution. What gives with the two different readings?
My chemistry;
Chlorine:1.8
Ph:7.4
Alkalinity: 80
Ch: 300
CYA: 25 or 80?
Copper: 0.4 I have a copper/silver ionization system for algae control which works great and allows me to keep lower chlorine levels and still have pristine water.

 

[woodyp]

Rule #1......"Trust your own testing". Welcome to the forum. You might read up on our suggestions of using that copper/silver system. Your FC is woefully low for your level of cya as well. See the chlorine/cya chart in Pool School.

 

[tim5055]

Yup, trust your testing. You care about your pool, the store cares about selling you stuff - the testing suffers due to many factors including poorly trained staff, trying to work too quickly or just outright dishonesty.

As woodyp suggested, do some reading in the Pool School. This site exists to arm you with the tools to make informed decisions on caring for your pool.

Welcome!

 

[engrav]

As I understand Taylor is 80 and pool store is 25.

What do you get if you use the reagent from the Taylor kit and the pool store test tube?
and
Did the pool store recommend that you buy some CYA?

 

[gadgetman9]

Thanks everyone for the responses and welcome. It's great to have such a helpful and knowledgeable group to bounce problems off of.

A note about the tests. Except for the CYA level, my tests match the pool store readings almost exactly. I do trust my own testing, just can't figure the CYA difference.

A note about the local pool store. The manager is more interested in helping her customers than selling stuff. A rarity and I feel lucky to have her in town. She gave me a gallon of the CYA test solution (I believe it's R0011 if memory serves me) and the test tube at no charge. I thought she might have been loaning it to me, but when I tried to return it to her, she wouldn't take it back or charge me for it. This is not the first time she has given me things for free. She has 20 years experience in owning, installing and maintaining pools, and frequently mentions looking online for a better price than in her store, like the filter grids which I found for a third of her price. It's good to have someone I can trust. She is at a loss as to why the CYA readings are different and has not tried to sell me anything to cure the problem. I like their test tube with the slide. It makes more sense to be able to vary the depth of the dot and be able to determine exactly where the dot appears or disappears.

woodyp, I've been using the ionization system for about 6 years and always kept minimal levels of chlorine. Just enough to oxidize the residual contaminants. Water is always crystal clear and people always like the low levels of chlorine, especially those who have a sensitivity to it. I didn't take pool chemistry seriously until 2 years ago when I bought the Taylor kit from Amazon, based on recommendations from the pool store lady. My alkalinity is still high because I used to use baking soday to adjust the PH after every rainstorm. I will search TFP for ionizer advice. I saw posting for SWG ionizors, but nothing for the copper/silver.

engrave, I have not used my reagent with their test tube, but now that you mention it, I will. Their tube takes much more of the reagent, hence her reason for giving me the gallon (for free).

 

[woodyp]

Man............if it's working for you, then......"PARTY ON GARTH"! The CYA test to answer your question----------there is a big difference in testing done under flourescent lights vs. natural outside sunshine with the sun to your back.

 

[gadgetman9]

OK, so I've rerun the CYA tests as follows.

Pool store test tube with their reagent
Pool store test tube with my reagent
Taylor kit with their reagent
Taylor kit with my reagent.
All done with same lighting in the same location.

Still getting the same readings. Taylor 80 ppm. Pool store test tube 25 ppm.

Since pool store analysis matches mine on all tests except CYA, I don't know which CYA test to trust. Seems I would need a third independent test, but where?

 

[nedchavez]

You could ask your pool person if she can get some R-7065 CYA Standard Solution.

Or order some from tftestkits.net

This standard should read 50 ppm CYA with whatever tester you use.

If you do, please let us know what you find!

 

[gadgetman9]

is this a premixed solution for testing the test kits?

 

[tim5055]

is this a premixed solution for testing the test kits?

exactly. Premixed to show a 50 CYA

 

[engrav]

OK, so I've rerun the CYA tests as follows.

Pool store test tube with their reagent
Pool store test tube with my reagent
Taylor kit with their reagent
Taylor kit with my reagent.
All done with same lighting in the same location.

Still getting the same readings. Taylor 80 ppm. Pool store test tube 25 ppm.

Thank you
Helpful for me to know that the variance does not derive from the sample or the reagent.

 

[gadgetman9]

You could ask your pool person if she can get some R-7065 CYA Standard Solution.

Or order some from tftestkits.net

This standard should read 50 ppm CYA with whatever tester you use.

If you do, please let us know what you find!

Ok, so I ordered the R-7065. Just to make sure, I use it straight and not mixed with pool water. I would use it as is to test the kit's accuracy, correct?

 

[nedchavez]

You are correct!

EDIT: Sorry, bad info. See jblizzle below for correct info!

 

[jblizzle]

Well, almost. You add the standard solution instead of pool water and then add the normal CYA reagent to it. The reading should be 50ppm ... so you need to find the lighting and arm position that gives you a 50ppm reading.

 

[JoanC]

I've had some good luck and not so good with my CYA testing both last year and this. This is quite worrisome.
Thanks to searching the forum for help in perfecting my TF-100 testing techniques for CYA, I found a thread suggesting the standard solution.
I should be receiving it today. However, I didn't think about the last part of jblizzle's post coming into play at all.
It makes sense that the standard solution would only show at 50ppm when in the ideal lighting situation which would include arm/hand tilt or height.
Finding that ideal lighting and so forth will tell you/me the ideal situation for an accurate reading using our pool water with the reagent.
Thank you for this added info which I should have thought of but didn't.

That's a, well DUH! on me.
Thank you again!

 

[PAGirl]

I find this quite interesting. Waiting to find out what happens.....