The Mystery of the Missing CYA

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A

Abnaxis

Well-known member
Jun 28, 2021
95
Indiana
Pool Size
6500
Surface
Fiberglass
Chlorine
Salt Water Generator
I recently discovered that my local pool shop stocks Taylor test kit reagents because "one of their big pool manager customers requested it."

It's been 2-3 years since I bought my TFTestkit Pro, and my old DPD powder got some moisture in it and is currently DPD brick, so I decided to buy replacement reagents for all my tests while I was buying other unrelated pool stuff.

Everything worked fine, except when I do the CYA test, the water turns out clear. Like, I can see all the way to the bottom of the tube no cloudiness at all.

So then I go back to my shelf and pull out my old bottle of R-0013 and try again. Same results. You can't even tell the water has reagent in it, you can see straight to the bottom of the tube when it's full.

This baffles me. CYA should only go down if you replace the water in the pool, yes? I was expecting it to go down a bit because I lose a lot of water any time I backwash my filter, but it shouldn't be zero...

Last year, I tried to use some ascorbic acid to clear up some iron stains on my pool, that wouldn't have done it? Did I just run the test with two bad bottles of R-0013?
 
Abnaxis said:
CYA should only go down if you replace the water in the pool, yes?
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It degrades between 3 and 5 ppm a month, which is unnoticeable during the season, but very noticeable when us northerners walk away from the pool for 6 to 9 months.

Those of us with mesh covers pick up a couple feet of rain in the off-season to dilute it further. I get 3 ft most years and historically closed at 70 CYA and opened with 20 at most.
 
JamesW said:
When was the last test?

What was the reading?
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11 months ago I read it at 70. I usually just check it once a year or if I'm replacing water. Historically--insomuch as the two years and change I've had this pool qualifies as "history"-- that's been enough.

Newdude said:
It degrades between 3 and 5 ppm a month, which is unnoticeable during the season, but very noticeable when us northerners walk away from the pool for 6 to 9 months.

Those of us with mesh covers pick up a couple feet of rain in the off-season to dilute it further. I get 3 ft most years and historically closed at 70 CYA and opened with 20 at most.
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If CYA drops without water replacement, that's news to me. My pool spends 95% of its time with a solid autocover for safety (I don't have a fence). It loses relatively little water to evaporation and gains next to none from rain. Most of my water loss comes from backwashing the filter.

If CYA degrades 3-5 ppm, where does it go?
 
Abnaxis said:
. I usually just check it once a year or if I'm replacing water. Historically--insomuch as the two years and change I've had this pool qualifies as "history"
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So. 3rd time's *not* the charm ? :ROFLMAO:

Did you ever use pucks / trichlor / dichlor that snuck some CYA in there ?
 
JamesW said:
CYA breaks down due to oxidation by chlorine and sometimes by bacteria.

View attachment 561542
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Ah, so it just kinda leaves as nitrogen gas and CO2? Sorry, I just always think it's interesting to look at what happens when pool chemicals get "used up."

Newdude said:
So. 3rd time's *not* the charm ? :ROFLMAO:

Did you ever use pucks / trichlor / dichlor that snuck some CYA in there ?
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I mean, to be fair my pool has been exceptionally easy on me. The only times my numbers are out of whack is when I mess up measuring something. I mostly just test to make sure nothing weird happened, it's practically pre-ordained what the result will be once the TA settles in (as long as i remeber to adjust SWG for usage). I thought CYA was yet another number that just sits there and tells me everything is normal.

Never used pucks, only jugs and SWG. Speaking of SWG, though: I, uh, kinda forgot to turn the generator off when I got the pumps running. My usual opening routine is get pumps running > check Cl > SLAM if needed > balance water > turn on SWG. Having the SWG running 10% with no CYA for 4-ish hours probably didn't break anything, right?
 
Abnaxis said:
Having the SWG running 10% with no CYA for 4-ish hours probably didn't break anything, right?
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The SWG only cares that you have flow, and enough salt for the magic to happen. If your FC burns off in 2 hours with no CYA, the SWG won't even know, much less care (y)
 

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ON TOPIC, it sounds like I don't need to go online and buy yet another bottle of R-0013, I should just gradually add CYA until it's right

COMPETELY OFF TOPIC, I would have thought CYA would change the electrolytic properties of the water. TIL the SWG only cares about CYA so the chlorine doesn't burn off
 
Abnaxis said:
TIL the SWG only cares about CYA so the chlorine doesn't burn off
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The SWG doesn't know or care. You care. You'll be adding FC every 2 hours with low CYA, or you'll get a swamp.


Add the remainder of how much you've added so far, to 30. You started with 0. Raising the CYA with tabs will take a couple weeks and won't end well.
 
The water is still 45F. As long as the cover stays on, I lose less than 1ppm FC a day.

Again, I've never used tabs. I tie a skimmer sock to some pool wire and dangle it in front of the jets. It takes almost exactly a 4lb container to hit 75 ppm, I'll probably do 2lb and 2lb again.
 
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I usually add enough CYA to get to 80 at the beginning of the season. In July I'll add a little more to get back to 80. Our swim season ends in Sept and I close mid October with a CYA of 50 ish. Between rain dilution and normal loss I am lucky if I start the year with a CYA of 20.

We've had a ton of rain this year. I'm expecting a non measurable amount of CYA when I open in two or three weeks.
 
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