Can shock skew CYA test results?

[mknauss]

I don't know what that means. I lowered the water quite a bit last fall, but what's there now is also tap water and rain water.

So the pool water had some CYA in it. From last year. So what you added this year added to what was in the pool.
If, after refilling this spring, the CYA was 20 ppm, which is not testable, then when you added 30 ppm worth you are now at 50ppm or so.

 

[Mdragger88]

Go with the higher cya reading for now- this ensures u are chlorinating properly & SLAM Process is effective. Hopefully u will see more success in your slam confirming your results.
It’s definitely possible the initial dose of cya wasn’t fully distributed in the water w/ the 1st test. Testing at least 24hrs after adding is recommended.
Are u certain of your pool’s volume? Testing fc after dosing can help u dial that in.
Also When slam is done & u need to adjust ph, testing where your acid addition actually landed u after about 30 minutes can be the most accurate way of really dialing in volume since MA doesn’t lose potency like liquid chlorine can so there’s less variables.
The standard solutions can be quite helpful for confirmation that you’re interpreting results accurately as well. Cuz pics on the internet aren’t quite the same as seeing something in real life.
Slam on

 

[DeptOfMeteors]

What is being suggested is that you do a test on a sample of water from the spigot/hose you are using to top off your pool...the "fill." It is not distilled so it's going to have its own pH level, maybe some calcium and possibly iron or other things. If the "fill" water contains too much of something that can only be corrected by draining then that's something you want to be aware of so you can plan and adjust accordingly.

Ah that. Well, I did do a CYA test in the spring and the dot was as clear as day all the way to the top.

It may or may not look a bit hazy to you. The frequently given advise on this site to do the CYA test is basically “stand in the bright sun with your back to the sun with the vial at waist height and glance at the vial”. That advice assumes everyone’s visual perceptions are the same across the board with no variations from individual to individual. For example, I have excellent night vision which means my eyes are very sensitive to bright light. When I stand in the bright sun with my back turned to it, the sun reflecting off my pool deck is enough to cause me a bit of snow blindness, and I can’t accurately make out the test. I personally have way more luck simply performing the test in the shade. If you KNOW what say 50ppm of CYA looks like to you and how it looks to you under different lighting situations, then you know what 50ppm is supposed to look like. The sampler simply teaches you what to look for.

So when the level gets to "50" and I can't see it anymore, some others might have the acuity to still see it, in which case my CYA would be lower than I thought I guess I could get a 3rd opinion next time I do the test. We're all myopic here though. But only one of us is partially colour blind (I fall over backwards on Ishihara tests).

 

[Steve-D]

So when the level gets to "50" and I can't see it anymore, some others might have the acuity to still see it, in which case my CYA would be lower than I thought I guess I could get a 3rd opinion next time I do the test. We're all myopic here though. But only one of us is partially colour blind (I fall over backwards on Ishihara tests).

If (as you said) you are handing off your sample for a 2nd opinion and you both agree on the reading then you can probably trust that.

 

[Orion7319]

Ah that. Well, I did do a CYA test in the spring and the dot was as clear as day all the way to the top.


So when the level gets to "50" and I can't see it anymore, some others might have the acuity to still see it, in which case my CYA would be lower than I thought I guess I could get a 3rd opinion next time I do the test. We're all myopic here though. But only one of us is partially colour blind (I fall over backwards on Ishihara tests).

Pretty much. Another example, some people can’t taste the salt in my pool,others (including myself) can. Yet another example, my wife can detect foul odors nobody else can smell from a mile away. Everyone is different.