Added CYA, test says it went down

[jefski]

Started with TFP early this month, working on CYA and alkalinity levels. CYA was too low to measure with the K2006. Last pool store test said 17. Added 4 lbs (in a sock) and it came to 27. 4 more and it was 44. 4 more and it's up to 63, 6 days ago. No additions this week so the filter could be backwashed. Tested this evening and it's down to 33. Tried 3 times.
I just got a new bottle of the test soln from TFTest (R0013, I think). Thought I used it for the 63 test (last log below), but that's been a while so it's possible that tonight was the first.
There have been no additions of water since adding about an inch 8 or 9 days ago following a backwash. The pool wasn't used this week, but the cover was open most days.
The only unusual event recently was cleaning behind the light. The back and niche were pretty slimy: white water mold is what we were told.
Any thoughts on what caused the drop?
Thanks

==========================================
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Build Type: Fiberglass
Volume: 14750 gallons
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Latest Test Result Summary:
FC: 7.4 (an hour ago)
CC: 0.4 (an hour ago)
pH: 7.2 (an hour ago)
TA: 145 (an hour ago)
CH: 380 (10 days ago)
CYA: 33 (an hour ago)
SALT: 3400 (19 days ago)
==========================================
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Chemical Addition 08-28-2021 @ 08:00 PM
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+ 48 FluidOunces of Baume31

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Test Results 08-28-2021 @ 07:45 PM
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Free Chlorine: 7.4
Combined Chlorine: 0.4
pH: 7.2
Total Alkalinity: 145
CYA: 33

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Maintenance 08-28-2021 @ 07:30 PM
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Backwashed

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Notes 08-28-2021 @ 12:02 PM
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I was away since 8/22. FC checked during the week with test strips. FC went to zero a couple of times. 3-4 gallons were added.

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Chemical Addition 08-28-2021 @ 12:01 PM
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+ 48 FluidOunces of Baume31

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Chemical Addition 08-28-2021 @ 11:45 AM
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+ 128 FluidOunces of Bleach (10%)

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Test Results 08-28-2021 @ 11:40 AM
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Free Chlorine: 2.0
Combined Chlorine: 0.3
pH: 7.4

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Chemical Addition 08-22-2021 @ 10:42 AM
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+ 32 FluidOunces of Baume31

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Test Results 08-22-2021 @ 10:39 AM
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Free Chlorine: 6.0
Combined Chlorine: 0.4
pH: 7.2
Total Alkalinity: 160
CYA: 63

 

[Texas Splash]

I guess our first question would be are all of those your CYA tests with the K-2006 or the pool stores? When using the K-2006, there are no specific or intermediate lines between the 10th or each level, so we round up or down. If it's halfway between 30 & 40, we call it 40. Pool stores try to get specific which doesn't matter since they are usually way off the mark anyway.

 

[jefski]

Those are all my tests with the K2006. So rounding, it looks like we went from 60 down to 30.

 

[PoolStored]

First, we would round up to the 40 level, not 30. I lose about 10ppm of CYA in 3 weeks. I cannot explain it, it just happens. This week, I lost 10 alone. And I'm good at reading it, and I have the standards to compare. Don't know what changes mine. It just does. Mine also takes a week for my CYA to show up when I add it. I think it may be due to the zeolite media in my sand filter. Again, don't know why, but that is what MY pool does.

Second, maybe related, why are you driving your pH so low? adding 48 ounces of MA when you pH is 7.2 would lower it to 6.4. I'm not sure that is wise. Other's may chime in, but I think it is better to keep in the 7s, even if you are fighting rising pH because your TA is so high.

If you are trying to reduce TA, then reduce your TA with MA, but only add enough to lower pH 7.0. Then aerate to raise pH back to 7.4, add enough MA to get back to 7.0, aerate. Repeat until you get your TA to your target level. Reason for 7.0 as a target, it keeps your pH safe, and CO2 outgasses (raising pH) at the highest rate between 7.0 and 7.4 Good Read: Lower Total Alkalinity - Trouble Free Pool There are also a bunch of threads on aerators.

Finally, have you downloaded PoolMath Can really help you understand the impact of what you are adding to your pool, before you add it.

Welcome to TFP!!!

 

[setsailsoon]

Something doesn't look right. You added 48 oz of acid and pH stayed the same? Should drop by .8 pH Are you doing the CYA test outside with sun to your back? Were all these tests done by test strips or something? About all I can tell from this data is that test strips don't work.

 

[PoolStored]

@setsailsoon He has indicated he is using K2006. I think he is selecting Baume31 in pool math, when in fact he is adding Bleach! The only thing that changes is his FC. I was confused too and had to read three times to figure it out. @jefski Can you confirm you are adding bleach and not MA?

 

[setsailsoon]

@setsailsoon He has indicated he is using K2006. I think he is selecting Baume31 in pool math, when in fact he is adding Bleach! The only thing that changes is his FC. I was confused too and had to read three times to figure it out. @jefski Can you confirm you are adding bleach and not MA?

Thanks Pool. Yeah, it's confusing with the note about using test strips and some of the results on 8/22 and the rest on 8/28. Jef, can you clarify?

Thanks.

Chris

 

[PoolStored]

Thanks Pool. Yeah, it's confusing with the note about using test strips and some of the results on 8/22 and the rest on 8/28. Jef, can you clarify?

Thanks.

Chris

My guess is that he was away and it was easier to teach someone test strips instead of the drop test. Just to have someone to add bleach, without confusing the heck out of them, or scare them away.

 

[jefski]

Sorry for the confusion. I was away for the week so my wife just used test strips to keep FC level up during that time (8/23 - 8/27). All the measurements are with the K2006.
About the MA additions: just before noon, pH was 7.4. My poolmath app said to add a little more than the 48 oz to get to 7.0, but I rounded to a quart and a half. pH only went to 7.2 about 8 hours later, so I added another 48 oz. I just checked the poolmath app again to make sure I didn't misread it. To go from 7.4 to 7.0, TA of 145, add 58 oz of 31.45%.

Interesting about your CYA dropping inexplicably, thanks for sharing that. I'll just keep adding to get to the 70-80 target. I've found some good and some bad reviews on the Aquamate CYA I've been adding.

 

[PoolStored]

58 ounces, in a 14,750 gallon pool should lower your pH by .9! Is your pool size setup correctly? Can you post a picture of the MA you are adding, I suspect it is not 31.45%, 20 Degree Baume. Something doesn't square.

Few lessons, I learned the hard way: 1) always read the label and know EXACTLY WHAT you are adding, and 2) know exactly WHY you are adding it and 3) what your expected result is and test for it...if it doesn't match, something is up...

 

[jefski]

It seems OK, what do you think? (BTW, I hope I'm adding the images correctly)

 

[PoolStored]

It seems OK, what do you think? (BTW, I hope I'm adding the images correctly)

This is good. If you go to "affects of adding" in pool math, it indicates the pH will drop by .9 with 58 oz. of MA. However they are approximately correct with TA between 80-120. Since you are 145, the effect of adding 58oz. will be lower.

Continue to use click pH from the overview with a target of 7.0 with an accurate TA and 31.45%, which you have been doing from second screen you posted above. When your TA get down to 60-80, you will see a reduction in the pH rise.

As your TA falls, the recommended amount of MA to add to reduce to 7.0 will fall. You are on the right track, the miss on my part was the TA. Forgive me.

On the CYA, yes, I have seen variation on the quality. One recommendation, when you find a quality product, add in increments of 10ppm or 20ppm and wait 24-48 hours before testing and adding more. I discovered my pool will take a week to get to target amount. I now trust Pool Math for amounts (with quality product), and I'm patient to wait for the results.

Sorry for creating confusion on the MA.

 

[jefski]

I really appreciate your help!!

 

[PoolStored]

I really appreciate your help!!

All good. Sorry on the MA confusion.

On the aerator front, I built this on top of a 1/2 horse sump pump, see post #4. DIY Aerator Put it in the shallow end. Kids love it and makes a soothing sound.

I have a 31K gallon pool. I can reduce TA by 10 and raise pH by .4 in 12 hours. Add MA to reduce to 7, aerate to 7.4, repeat. I went from 140 to 70 in about 3 days. I then added 50ppm borates using duda diesel granular boric acid. I haven't added MA in two months. Family loves the borates.

 

[setsailsoon]

Jef,

I actually put in the TA on the desktop version. I guess this calculation doesn't pick up the TA like the phone app does. Sorry for the error on my part. Pool, thanks again.

I ran my TA about 50 and it helped control pH a lot but still too many adjustments were needed. Then I added borates to 50 ppm. Worked just like @PoolStored . I found the test strip method for borates to be pretty worthless so I bought a couple more reagents and used them with a few test kit reagents for a drop test that was very easy. Here's more info on borates in case you're interested.

Chris

 

[jefski]

Thanks for the info, Pool and Chris. I'm planning to add borate, but thought I should bring CYA and TA to the proper levels first. Does that make sense?

On the aerator front, I built this on top of a 1/2 horse sump pump, see post #4. DIY Aerator Put it in the shallow end. Kids love it and makes a soothing sound.

I have a 31K gallon pool. I can reduce TA by 10 and raise pH by .4 in 12 hours. Add MA to reduce to 7, aerate to 7.4, repeat. I went from 140 to 70 in about 3 days. I then added 50ppm borates using duda diesel granular boric acid. I haven't added MA in two months. Family loves the borates.

I added a little waterfall fountain from Home Depot a week ago for aeration, not sure it's doing much. Not seeing TA change anything like you did. Time for another trip to HD.

 

[PoolStored]

Yes, get the chems right first. CYA, not so much, but certainly TA. TA MUCH harder to change after you add borates.

On the aerator front, I have learned a lot. You want a lot of small bubbles, and the amount of air time (time the water is in the air) both increase the outgas rate. If I had to do it over, I would rebuild the one I have and orient the nozzles to spray out, horizontally across the pool, rather than down. Either way, it is effective.