pH going up

[da5487]

Hey TFPC community,
Thanks for the great site and helpful info! I moved into a house with an in-ground pool/spa with spillover a while back. Because of this site, I transitioned the pool this summer to manual dosing of 10% liquid chlorine. After years of trichlor tabs for this pool, the CYA had reached the 160 range. I did a few partial water changes over the summer and brought CYA down to 60. I used to have a pH that went down due to the trichlor tabs. Not any more. So, that's where my question comes in. pH is constantly creeping up. I am routinely bringing the pH down from 7.8 to 7.4 once to twice per week. My understanding is that the liquid chlorine has a net zero effect on pH, so long term (over a week) this should not be the cause of the pH increasing.

Questions:

1. Is the aeration from the spillover (my only source of every day aeration) enough to move the pH up this fast? (is it normal to add acid like this twice per week?)
2. Is there a way to make the pH more stable?

Here is some info about the pool and my testing
17,000 gal in-ground plaster pool with spa and spillover
FC kept in 4-7 range
CC near zero
pH 7.7
TA 80
CH 260
CYA 55
temp 78
currently the daily FC replacement dose is around 2.0
I most often use a LaMotte ColorQ 2056 test kit - I also use a Taylor k-2006 (C) kit. I've recently had a bit of an offset between the two kits for pH (LaMotte might read 7.6 when Taylor reads 7.8). This morning, however, they both seemed to agree on 7.4 after adding acid to the pool.

thanks for your help!

 

[Texas Splash]

Hello and welcome to TFP! There are a few sources of rising pH that include:
- New plaster
- Aeration (Spa/spillover, SWG, waterfall, even lots of splashing)
- Elevated TA

While your TA is not high by typical standards, you do have the option to bring it down some more, That might help keep the pH more stable. I would suggest lowering your TA in increments of 10 first to 70, then 60, maybe even 50. You might be surprised how better your pH stays constant. Are you familiar with the acid/aeration method? Try this page: Pool School - Lower Total Alkalinity.

Hope this does the trick for you. Have a great day.

 

[pabeader]

Just a quick note: The Taylor kit is by far the more accurate in relation to the LaMotte. There are issues related to the calibration of the color sensors and other things. A quick search around the forums here should produce a number of threads related to this.

 

[da5487]

Hello and welcome to TFP! There are a few sources of rising pH that include:
- New plaster
- Aeration (Spa/spillover, SWG, waterfall, even lots of splashing)
- Elevated TA

While your TA is not high by typical standards, you do have the option to bring it down some more, That might help keep the pH more stable. I would suggest lowering your TA in increments of 10 first to 70, then 60, maybe even 50. You might be surprised how better your pH stays constant. Are you familiar with the acid/aeration method? Try this page: Pool School - Lower Total Alkalinity.

Hope this does the trick for you. Have a great day.

Thanks for the reply, Texas. So, new plaster is not the cause this time, but that is good to know. The spillover is my likely source. It is one foot wide and the water falls about 2 feet from the spa into the pool. The elevated TA is really what motivated my post. Yes, I did read and use the acid/aeration method to bring the TA from 120 down to 100. TA was higher when I was using trichlor tabs. I brought it down to 100 over several days using this method, and my guess is that this acid/aeration mechanism has been at work since then but at a slower rate. The TA has come down from 100 to 80 over a few months time without aggressively lowering pH to 7.0-7.2 and adding more aeration to the pool (which is what I did from 120 to 100). I've simply been lowering pH to 7.4-7.5 when it hits about 7.7, and over 3-4 days it rises back up presumably due to the spillover.

Since I did read that acid/aeration instruction you linked, I had expected the pH to be more stable by now at 80. To your point, I'll work toward a lower TA and see if pH drift slows down. Thanks again!

pabeader: thanks for the note. Yes, I agree the colorq can be off. The TA is just off at this point and has been all summer. Not to divert this thread onto measurement or anything, but mine starting reading TA 80 when it was 120 according to multiple other sources. I don't know why it is off so much, but I stopped checking TA from colorq since then, I use the Taylor. I did try fresh reagents, but that was not the problem with colorq TA. I like the speed and simplicity of the colorq for daily use (FC and pH) as long as the numbers check out against another system. So, I check them against the second system on a weekly basis when I do more comprehensive testing.

thanks again!

 

[JoyfulNoise]

da5487,

You've been given great advice thus far and I don't want to add to the information overload. However, I will add this, once you get your TA lower (around 60ppm) see how the pH stability goes. If you still feel like you're adding too much acid for your liking, you can also try adding 50ppm borates to your water. Borates act as an additional buffering system for pH and many TFP'ers have found them to be very useful in controlling pH. They don't decrease the amount of acid you add (you wind up adding a greater amount of acid just less frequently, total amount of acid stays constant) but they do extend the period of time between acid additions. Borates are definitely an optional chemical to add and should only be added once all other avenues are exhausted - reduced TA, reduced cycle time of aeration sources, higher pH targets, etc.

And where are my manners.....Welcome

 

[da5487]

da5487,

You've been given great advice thus far and I don't want to add to the information overload. However, I will add this, once you get your TA lower (around 60ppm) see how the pH stability goes. If you still feel like you're adding too much acid for your liking, you can also try adding 50ppm borates to your water. Borates act as an additional buffering system for pH and many TFP'ers have found them to be very useful in controlling pH. They don't decrease the amount of acid you add (you wind up adding a greater amount of acid just less frequently, total amount of acid stays constant) but they do extend the period of time between acid additions. Borates are definitely an optional chemical to add and should only be added once all other avenues are exhausted - reduced TA, reduced cycle time of aeration sources, higher pH targets, etc.

And where are my manners.....Welcome

thank you, all great info! I will also reduce my pump cycle time, that should help. good point!

 

[Agent99]

Well, darn it...I have nothing to add here except that I have new plaster (7/15) and I do add about a quart of 31.45% MA per week to take it from 8ish back to 7.5ish. I think I'm just going to let my TA drift back down again and see if that'll help but I think the new plaster will fight me until next summer!