Rising pH and Creeping TA

[Naplespool]

Our pool water is sparkling, no problems.

I am trying to better understand the source of my pool's daily rising pH and slightly creeping up TA. Pool is plaster with embedded small pebbles. It is one year old. The current pool chemistry is:

CL 6.5
CC 0
PH 7.8
TA 80 (acid drops the TA but then it creeps up 10 ppm over the following week)
CH 450 (up from 400 three weeks ago)
CYA 70-80 (stable)
Salt 3650 (stable)
Borate 48 (manitol tested)
Temperature 84

In the past 6 days, I've added no water and we've had no rain. I have physically unplugged the Salt cell. Pump runs at 2000 rpm, all water features off, there is just the slightest movement on the surface. There are no bubbles entering the pool at the returns. I have been dosing the pool daily with 16 ounces of 15% chlorine bleach as the 17,250 gallon pool uses about 1-1.5 ppm chlorine per day.

Two days ago the pH tested 7.6, yesterday the pH tested 7.7 and tonight it tested 7.8. My understanding is that CO2 outgassing is the primary culprit in pH rise. With the situation as I've summarized it, does my pH rise sound like CO2 outgassing or something else and if so what would that be? Thanks in advance for any ideas.

Naples Water (shut off for the last 4 days, evaporation less than an inch)
pH 9.25
CL 0.4
CC 3.2
TA 30
CH 50

 

[Jimrahbe]

np,

So how long does it stay at 7.8 or 7.9?

All pools are different of course, but my pool seems to like 7.8.. it will stay to 7.5 for about a microsecond, but will stay at 7.8 or 7.9 for a week, or weeks, depending on the time of the year.

Thanks,

Jim R.

 

[JamesW]

If the pH, TA and CH are all rising, then you're probably getting some calcium carbonate from scale or the plaster.

If you have any scale, try to keep the CSI about -0.3 until all scale is gone.

If you have zero scale, try to keep the CSI at about -0.1 to 0.0.

 

[Naplespool]

np,

So how long does it stay at 7.8 or 7.9?

All pools are different of course, but my pool seems to like 7.8.. it will stay to 7.5 for about a microsecond, but will stay at 7.8 or 7.9 for a week, or weeks, depending on the time of the year.

Thanks,

Jim R.

I am going to figure that out. It is 7.8 this morning.

If the pH, TA and CH are all rising, then you're probably getting some calcium carbonate from scale or the plaster.

If you have any scale, try to keep the CSI about -0.3 until all scale is gone.

If you have zero scale, try to keep the CSI at about -0.1 to 0.0.

I’ve been worried that the plaster is the culprit. I’m not aware of any scale. For instance the salt cell had only a tiny amount after a year. It is a pebble tech type called silver pearl I believe and seems rough. The csi has been well in range for a year. Is there something I can do to tell or to harden it now?

 

[JamesW]

Mostly just maintain good chemistry and brush. I would keep the pH at 7.8.

 

[Naplespool]

Thanks, I do the chemistry and my pool company does the cleaning. They vacuum every week but I can't remember seeing them brush.

Why is brushing important to these issues?

 

[mknauss]

Brushing cleans debris that sticks to the wall surfaces, it disturbs any biofilm on nascent algae, it mixes the water in the low flow/dead zone areas of your pool.

A robot does the same. Though it cannot get to certain corners, steps, or shelves.

If your pool cleaning service is not brushing, they should. Mine does. And as with you, they do not add chemicals, excluding acid to maintain our pH when we are gone for extended periods.

Take care.

 

[Naplespool]

So back to my main investigation, I had the fill water off and the salt water generator electrically disconnected for the past 5 days. Here are the pH readings:

7.6
7.7
7.8
7.9
8.0

Since It hit 8.0 today I added acid and brought the pH to 7.5 today (dropping TA from 80 to 60), turned on the fill and salt cell (since that didn't really matter) and will start brushing the pool daily after this weekend.

If anyone has insight into the rising pH (plaster defect, incorrect hardening procedure) or any other steps I should take, it would be most appreciated.

 

[JamesW]

There might some reason that your plaster is weak and dissolving or you might have scale that's dissolving.

If you're sure that you don't have scale, I would recommend that you keep the pH at 7.8, not 7.5

Are your calcium and TA levels increasing?

Can you show a picture of the pH test when you think that it's at 8.0?

Are you brushing the pool regularly?

 

[jstephens24tx]

your TA reading drops instantly by going to 7.5? Iv been in the process of lowering mine and its been a slow process