PH dropping without adding any Acid

[bwillick2015]

Hey Everyone. Looking for a little help understanding why my ph is dropping. This is second year I have had the pool, it's 17,500g fiberglass ( i do have pool math app but dont know how to share my data from there) I run SWG hayward T3 running at 45% woth a variable speed pump that runs 24/7 at 3 preset speeds to turn over my pool water 3 times a day. Last year my ph always wanted to hang out around 7.8 for 2 or 3 weeks then slowly start climbing up , so I would add little muratic acid bring it back down to say 7.5 to 7.6 within few days it would be back up to 7.8 and stay there for 2 or 3 weeks and then repeat. The rest of my chemistry from last year to this is basically the same and i set my CH level to account for a ph last year of 7.8 to keep my csi in check. I understand when I add stabilizer or we get lot of rain ( inground pool) that this will drop the ph proportionally, but my ph was 7.78 , 7 days ago and now today down to 7.52 and really nothing in my opinion that should account for that minimal rain ( comparing to last year rains would not dramatically change my ph unless we got alot ) The only thing remotely different is maybe having the solar cover on more often this summer but from all the googling I have done the only thing having the solar cover should do is slow down the rise of ph and from what i rememebr reading before pH should naturally always want to rise in a pool with a swg due to the reaction. Tje last time I added stabilizer was like 20+ days ago and at that time it dropped the ph down to 7.5 or 7.4 and then came back up to the 7.78 before this weird crashed happened. For testing equipment I use taylor drop test kit but I am an instrument and Electrical tech at chemical refinery and I do all the calibrations of the analytical equipment so I have avaliable to me industrial grade ph meters that I calibrate regular with buffer solutions so whenever I get weird ph numbers I bring a sample into work to check it so I know I am accurate to two decimal places. Also while it has been warm here it's not enough to any degree that I have to top up my pool with tap water the periodic rains we get usually keeps my level perfect.

Any thoughts by anyone ? I would fine it hard to believe after 20+ days there is any trace residual stabilizer still in the system breaking down special when the ph already went back up to 7.8 before coming down and we haven't got much rain in last 7 days so kind of a little stumped on what would cause it.


FC:7
CC:0
TA:80
CH:250 ( last year I was closer to 275)
CYA: 60 ( normally 70 to 80, 2 weeks ago got a bunch of rain and just haven't topped it up)
Salt: 3200

 

[PoolStored]

7.78 , 7 days ago and now today down to 7.52

Did the Phenol red show this drop also?

rememebr reading before pH should naturally always want to rise in a pool with a swg due to the reaction.

SWG is pH neutral.

 

[bwillick2015]

Did the Phenol red show this drop also?

SWG is pH neutral.

Yes the red drop test also showed it to be in that range obviously I can only eye ball when doing that so I can only say if it looks more like 7.4 or 7.6 etc but I do usually follow it up with a drop of acid demand reagent to see what bar it drops it down to as a confirmation ... so that's why when I do Get something I don't expect I take a sample to work for more accurate analysis .... it's almost as if something is leaching in to the pool but I csnt explain what

 

[PoolStored]

Do you use borates?
What was your TA last year?
What other chemicals have you added?

So, this has happened to me this year. I have been mulling it over for about the last month, and was about to post it in the Guide/Mod/Expert forum. Might as well haul it out here.

I added CYA to a 7.6 pool. As you described, pH went to 7.4 as expected. Pulled out my trusty aerator and raised it to 7.8. I too use a cover, and always have. pH reverted to 7.6, and has been very stable at 7.6.

I suspect, in my case and in your case, that pools just find the balance between pH and TA. I suspect your TA was higher last year. High TA and Low pH are the drivers of pH rise. As you managed your pH, I suspect your TA has come down. When TA is 50-80/90 pH will trend toward equilibrium with TA level. Your pool likes 7.5 with a TA of 80.

Let's see what @JoyfulNoise has to say...

PH TA Relationship - Further Reading

www.troublefreepool.com

 

[JoyfulNoise]

Let it ride and see where it goes. I suspect this is more just testing issue than anything else. You really can’t transport a water sample without disturbing the pH. As long as your TA isn’t dropping then it’s not likely anything is being added to the pool. Your pH won’t crash when there’s appreciable TA so I wouldn’t worry about that.

 

[bwillick2015]

No borates, TA last year was about the same , only thing I see different in my last years numbers is I ran my chlorine at basically the bare minimum for my cya level ie 3.5 to 4 FC .... the last month now I have been running my chlorine more in the mid range of the recommend 7 ish and last thing I added 9 days ago was some salt to bring up my salt level which I shut the swg off over night added 20 lbs of salt mixed and let it sit 12 hours overnight before turning swg back on nut numbers were stable a day or two after


Thanks guys for the information. I wasn't super worried about it being a problem as my ph has never been outside of 7.2 to 7.8 since I have owned the pool I'm usually pretty diligent with testing but just couldn't quote explain why it was it doing that. The only upset is that it throws my csi out of whack driving it past the -.3 negative as I have balanced all my other chemicals based on closer to 7.8 steady ph. I will keep and eye and see what happens


I did not know transporting would cause much effect on the ph thanks for the info. I knew chlorine is affected due to loss in open air as our water treatment company always puts big emphasis on our operators doing our cooling water chlorine tests right away after taking samples

 

[JoyfulNoise]

I did not know transporting would cause much effect on the ph thanks for the info. I knew chlorine is affected due to loss in open air as our water treatment company always puts big emphasis on our operators doing our cooling water chlorine tests right away after taking samples

Really depends on how you transport it, what sample container materials are used, is it exposed to light, does it got hot, does it get jostled around a lot … that sort of stuff.

Usually you want to test right at the source of extraction or very shortly after that if what you’re looking for is a chemical that is reactive, eg, chlorine, or can have a significant equilibrium with its own gas phase, eg, carbonate/CO2. As long as the same collection and transport procedures are used, it’s fairly easy to eliminate or measure the effects. “Squeaky Pete” thrusting the sample bottle into the collection tank at arms length deep and shoving it in his back packet while he walks it over to lab, but not before stopping by the rest room to relieve himself of his morning coffee, probably isn’t the best approach.