What can throw off a CYA test?

[SCarolina]

Question about doing the CYA test correctly. It seems subjective with variation due to light conditions and how well you see the dot. Do you see it clearly, at a glance, etc. Are there some guidelines or is there a better test? I have added enough CYA to bring the levels up to at most 35ppm, but I get a reading of 60 with the dot test. Would one of these other additions change the test?

I just opened our pool after a difficult installation.
We are on a well with very soft water and I added 20 mule team borax to get our very low pH water up. So for my ~15,000 gallon pool I have added:
455 oz borax (Works out to about 26 ppm) I am going to use baking soda going forward for less drastic corrections.
about 70oz cyanuric acid (64 ounces from direct addition and the rest from floating 4 pucks)
2.5 total gallons of bleach added at different times for FC at first
50oz muriatic acid to back the pH down because I overshot a bit on the borax.
400 pounds salt pellets
We are using a SWG now so I shouldn't need pucks or bleach unless something goes wrong.

My numbers are
7.4 pH
90 TA
7.5 FC
0.5 CC
60 CYA !!
20 CH

I have added at most 35ppm CYA, so why is the test reading 60?

 

[mknauss]

Unless you have an unusually deep above ground pool, your volume of 15000 gallons is too high. At 4 feet of water depth, it would be 13500 gallon.
At that volume, you have added right at 50 ppm. The resolution of the test is +/-10 ppm.

Use 60 ppm CYA for your FC. Test in another few weeks and see where you are.

 

[Texas Splash]

Along with Marty's notes above, maybe this will help with your testing ........

CYA Testing:
Proper lighting is critical for the CYA test, so you want to test for CYA outside on a bright sunny day. Taylor recommends standing outside with your back to the sun and the view tube in the shade of your body. Use the mixing bottle to combine/gently mix the required amounts of pool water and R-0013 reagent, let sit for 30 seconds, then gently mix again. Then, while holding the skinny tube with the black dot at waist level, begin squirting the mixed solution into the skinny tube. Watch the black dot until it completely disappears. If it helps, pour a little, look away, then look back and pour some more. Once it disappears, record the CYA reading. After the first test, you can pour the mixed solution from the skinny view tube back to the mixing bottle, shake, and do the same test a second, third, or fourth time to instill consistency in your technique, become more comfortable with the testing, and validate the CYA reading. If you are still questioning your own results, have a friend or two do the same test 2-3 times. Share your results only after everyone is done to see if you came up with the same average results.

 

[Divin Dave]

How you hold the skinny tube will effect the test also. nt The CYA test is sensitive to the amount of light that enters the tube. If you hold it with several fingers, the light cannot penetrate the tube. Holding it differently with different numbers of fingers will effect the test.

Do the test the same way every time. Hold it with your thumb and 1 finger so you dont restrict the light entering the side of the tube.

 

[SCarolina]

Thank you for all the great comments. The pool wall height is 54". Not completely sure about the volume. I will retest holding the tube carefully and on a sunny day with my back to the sun. It is great to point out that I can repeat the test if necessary using the same water. Does the dot completely disappear with no visibility even with careful scrutiny? There is no you don't see it when you glance kind of thing?

 

[Bvacchiano]

Buy the 50 ppm STANDARD solution from TFT. Do this test RIGHT before you do your pool water test. This way you will know exactly what to look for in terms of the “dot” disappearing. Also obviously do it standing in same position as Standard solution test. Keep everything the same.

What I do is fill to 90 on test tube can see dot. Great! Fill to 60 can’t see dot. Awesome! Your CYA is between 60 and 80. Perfect. Keep FC at 6. Go swim in your pool.