Inconsistent CYA readings

#1
Hi everyone... I'm a new pool owner. I recently purchased a house with a pool and I have no idea what I am doing. I just received my K-2006 test kit but I am not sure if I am getting correct CYA numbers. Every other test were pretty consistent between my results, Leslie's pool, and the aquacheck strips. I'm not sure which results to use, mine or Leslie's.

Over the weekend, I went to the local Leslie's to test my water and here is what I got on 4/1:
FAC: 4
TAC: 4
CH: 300
CYA: 60
TA: 80
pH: 7.5
TDS: 1400
Pho: 100

Results with Aquacheck strips on 4/1:
TH: between 250-500
TC: between 5-10
FC: 5
pH: between 7.2-7.8
TA: 80
CYA: between 50-100

My own test results on 4/2 after adding roughly 170oz of 8.25% bleach on 4/1.
FC: 7.6
CC: .4
pH: 7.6
TA: 80
CH: 320
CYA: 120 1:1 diluted (Aqaucheck strips showed less than 100 CYA)

My results today 4/3:
FC: 5.5
CC: .5
pH: 7.5
TA: 80
CH: 330
CYA: 90
 

dsmith99

Silver Supporter
Jun 18, 2016
236
SW, Iowa
#7
After your sample and reagent is mixed up you can run the test multiple times if you need to, just pour the contents of your tube back into the sample bottle and run the test again.

This way you can try again to see if your result changes, view it under different lighting or you can even have someone else give it a try and see what they get.
 

Divin Dave

TFP Expert
LifeTime Supporter
Oct 2, 2013
5,194
Longview, Texas
#9
Also, to add, .... the water needs to be at room temp or above when testing for CYA. If the water is below 70 ish, bring it inside and let it warm up before testing.

When testing CYA, the light conditions are very important. Always test outdoors in a sunny spot with your back turned to the sun. Also, when holding the test tube, hold it with only 1 finger and your thumb. Holding it with multiple fingers restricts the light from shining in through the side of the test tube and giving you an accurate result.

Also hold the test tube at waist level when adding the solution and viewing the black dot.

The measurement accuracy of this test is about +/- 10 ppm,
 

Scoop

LifeTime Supporter
Jul 13, 2012
180
Dallas, TX
#10
's about CYA testing.

I try to test my CYA when the sun is at it's meridian ± ~ an hour or so (testing only on clear days) on the day I test, to test when sunlight is at or close to its maximum level.
 

FLPoolDIY

Well-known member
Aug 29, 2016
102
Land O Lakes, FL
#12
I've done the CYA test multiple ways and typically have the same result.

How I've done my test:
1. Indoors held test tube at waist level and filled while glancing at black dot until no longer visible
2. Indoors filling to each line and viewing at waist level until black dot is no longer visable.
3. Placed tube on counter on a white piece of paper and filled to each line until the black dot was no longer visible
4. Outside as defined on the instructions

I've done all four with the same sample and had the same result. I think the key is to have bright enough lighting/sun for the test to be valid.

As an added sense of accuracy I've used my ColorQ digital tester for CYA and its been within 10 ppm of what I visually identified with the test tube.

When I first started doing this test it would drive me nuts 🥜 looking for the black dot to disappear.

My neighbors were always curious what I was mixing in the little tube when I first started testing outside.