CYA is down. Doesn't make sense?

[SouthernHiker]

I just got home from a 9 day trip. Before I left the pool numbers were perfect. FC=4, PH of 7.6, CYA 70, borates 30. CC 0

I left the pool running 24/7 while gone and had a pool cover on it. The mistake I made was in mis-estimating my SWG percentage. So my FC dropped more than expected. It was at a 2 today, but PH was still at 7.6. So I had a green floor. The really odd measurement was my CYA dropped down to 40. I couldn't believe so also had it tested at pool store to confirm. How could my CYA have dropped from 70 to 40? It's been raining pretty steady, but nothing too crazy?

Does this seem odd to anyone else?

 

[OTPirate]

That seems a little excessive, even with the rain. How are you testing your CYA? The pool store is notorious for being way off with CYA testing.

 

[SouthernHiker]

I used my test kit with the black dot on the bottom first. For me, it seemed to have dropped to 50, they got 40. I'm going to test it one more time, and see if that could explain it.

I was reading about CYA degradation on here for the past few minutes, and saw an article about anaerobic degradation when combined with bacteria. Is it possible the solar cover combined with my FC getting low enough to allow the algae growth on the floor could have led to that kind of degradation?

 

[domct203]

I used my test kit with the black dot on the bottom first. For me, it seemed to have dropped to 50, they got 40. I'm going to test it one more time, and see if that could explain it.

I was reading about CYA degradation on here for the past few minutes, and saw an article about anaerobic degradation when combined with bacteria. Is it possible the solar cover combined with my FC getting low enough to allow the algae growth on the floor could have led to that kind of degradation?

Over 9 days, doubtful. I imagine you would also have a very high chlorine demand from that conversion.

 

[spinPHD]

3 explanations:
1. Test before you left was wrong.
2. Test when you returned home was wrong.
3. Someone drained and refilled about 40% of your pool while you were gone.

 

[borjis]

Have you had a ton of tree pollen falling in the pool during that time?

Reason I ask is, I lose 20ppm of CYA every year when the pollen drops in
from a neighbors tree. I don't know exactly how long it takes, I just know
that if my cya is 50 in march, it will be 30 by may 1st. like clockwork. Rain or no Rain.

It's a VERY odd phenomenon but it does happen.

 

[SouthernHiker]

3 explanations:
1. Test before you left was wrong.
2. Test when you returned home was wrong.
3. Someone drained and refilled about 40% of your pool while you were gone.

Haha to number 3. It definitely wasn't that one. and several tests for the weeks leading up to Number 1 would have had to have been wrong including both mine and the pool stores. So that leaves Number 2 as the only possibility. I just went to test again, and realized I am out of CYA testing agent. Going to have to order more, and maybe get someone else at the pool store to check it in the meantime later today. I just can't believe it would've gotten that low.

 

[domct203]

Have you had a ton of tree pollen falling in the pool during that time?

Reason I ask is, I lose 20ppm of CYA every year when the pollen drops in
from a neighbors tree. I don't know exactly how long it takes, I just know
that if my cya is 50 in march, it will be 30 by may 1st. like clockwork. Rain or no Rain.

It's a VERY odd phenomenon but it does happen.

I would suspect you are also backwashing/topping off more often from this pollen, which would be the more likely reason for the CYA drop.

Otherwise I'm coming into town to get me a truckload of this CYA reducing pollen LOL.

 

[SouthernHiker]

I do have some pollen that drops, nothing that seems to require me to backwash more often than normal. Again, though, I have been gone for 9 days, so no backwashing has occurred until today. I have another theory, perhaps when I took the solar cover off I mixed a lot of fresh rainwater sitting on top of it with the top layer of the pool water and I'm getting a bad result from mixed freshwater and pool water sitting on the top levels of the pool where I'm pulling my sample from. Going to test again as soon as new agent comes on. Didn't realize I was so low.

for now, is that 40 level going to hurt anything if it were true? I don't want to add any stabilzer until I know my results are correct.

 

[borjis]

I would suspect you are also backwashing/topping off more often from this pollen, which would be the more likely reason for the CYA drop.

Otherwise I'm coming into town to get me a truckload of this CYA reducing pollen LOL.

That's the very odd part, I'm not backwashing or replacing any water.
I was completely baffled the first year living at the house when it happened.

I have a theory it's something in that pollen from the neighbors tree and perhaps some other factors in play.
If I have a diving mask on and look up from the deep end, I see a ton of pollen
on the surface, but otherwise can't see it so well if looking down from the deck.