Turned pool from black swamp to crystal clear, but now getting odd CYA numbers...

dcrowdus

Member
Mar 24, 2017
20
Auburn, AL
I bought a house in the fall, let the pool turn to a swamp over winter. Then I binge-educated myself on this site and some others. Using Taylor kit for testing.

Started with a CYA of about 100. SLAMmed for weeks going through dozens of jugs of bleach. Pool got clear, added salt, now working on getting the generator tweaked to maintain the FC levels I need.

So that's where I'm at. However, last week when I tested, my CYA seemed to be around 50 ppm. It was 100 before I started slamming. This was a maybe 5 weeks ago--ish. I thought maybe the bright bathroom lighting was causing me to see the black dot easier.

Today (I was out of town for awhile) I did a full round of testing and the black dot won't seem to go away. It looks like CYA is around 30-40. This time I checked both bathroom lighting and in direct sunlight.

Since apparently the only way to reduce CYA is by dilution, is it possible that I lowered it that much in just a couple of months just by rain and topping off with hose water? I was backflushing around once per day for a couple of months, but its not like I let the backflush run for a long time. Just until the discharge turned clear (few minutes maybe).

At this point I feel like I have no confidence in my CYA numbers. Thus I have no idea what level do drop my FC to. With only the generator running the past week, I'm at about 12 FC right now. Way too high for only 30 CYA. I was going to target around 7 FC when I thought my CYA was closer to 100. But now I don't know. I don't want to make the mistake of adding more CYA again, only to find out I wasn't doing something right and end up with super high CYA levels.

And advice would be much appreciated. This site and forum has been of great help to me and I appreciate the time spent by everyone helping others.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
At this point I feel like I have no confidence in my CYA numbers.
You nailed it! That's your #1 issue right now. Try this:
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. 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 find the CYA to be close to or over 100, then do this as well:
CYA Dilution Testing:
Add pool water to bottom of sticker.
Add tap water to top of sticker.
Shake.
Pour out half so mixture is to bottom of sticker.
Add reagent to top of sticker.
Shake.
Test outside with back to sun and tube at waist level.
Pour back and forth a few times to see if you get the same result.
Double the result.
So confirm that CYA for us and we'll be able to help you get on track. :)

- - - Updated - - -

Also let us know .... are you on city water or well in Auburn?
 

OTPirate

Admin
In The Industry
Oct 2, 2013
1,345
Creedmoor, NC
You can try using the CYA standard R-7065 by Taylor. It is basically "pool water" manufactured with a set CYA of 50 ppm. So, you use the standard like it is pool water and you are able to test your reagent and/or your testing methods.
 

dcrowdus

Member
Mar 24, 2017
20
Auburn, AL
City water. I'm actually a civil engineer for the city here, so I can touch base with the water engineer and get some info on their numbers. When my initial CYA readings were close to 100, I did do the diluted test and confirmed that it was right about 100 and not higher.

I'll test again using the method above and try to stick to that method. The only problem I had with that before was needing the info on days that weren't sunny.

Our city does some pretty accurate rainfall measurements with gages spread across the city. I may get that info and crunch some numbers on on the amount of rain we have gotten over the past 5 weeks or so, then run some evaporation calcs and backflow discharge estimates. It will be approximate in nature, but I'm curious how much water I have inadvertently replaced since my initial measurements.

Thanks for the response.

One more thing, will FC 12 affect my pH readings? I had around 7.8 pH last week and added some acid. This week it is clearly 8 (or higher? does it stay red8 even if its off the scale?). We got a lot of rain the past week, so maybe that's why.... or the FC is making it inaccurate... or both. So many variables!

- - - Updated - - -

You can try using the CYA standard R-7065 by Taylor. It is basically "pool water" manufactured with a set CYA of 50 ppm. So, you use the standard like it is pool water and you are able to test your reagent and/or your testing methods.
That's pretty cool. I will try that. I would love to "calibrate" my testing method.

Thanks for the info!
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
One more thing, will FC 12 affect my pH readings?
It sure will. When FC is over 10, it tends to skew the pH and make it higher. That of course is one of the drawbacks of having a high CYA that requires a high FC level. Also remember that evaporation in itself will not lower CYA. Of course numerous backwashes and water replacement will over time. Definitely make sure it's a bright sunny day when you do the re-test on the CYA. It makes a big difference when looking down into the viewing tube at the black dot. Have a nice day.
 

dcrowdus

Member
Mar 24, 2017
20
Auburn, AL
Yea, I didn't necessarily mean evaporation directly. But trying to determine how much total water loss I have had (evaporation and backwash). Then I can assume that much water with 0 CYA was added back (rain+hose) and estimate how much it has been diluted over the past 5 weeks or so.

UNLESS, evaporation only removes water and not CYA, causing an increase in CYA ppm??? In that case I guess when I add back the same about of fresh water, the CYA ppm would be right back to where it was before evaporation. Does anyone know if the CY acid evaporates with the water, or does it leave it behind?
 

dcrowdus

Member
Mar 24, 2017
20
Auburn, AL
Okay, thanks for the info once again. I feel like I will never know everything there is to know about pool chemistry. Of course that wouldn't be any fun anyway.
 

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