Sanity Checks on Plaster SWG pH Rise in 2nd Year Pool

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DB-Cooper

DB-Cooper

Well-known member
Jun 18, 2019
594
Austin, TX
Pool Size
30000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Hi team,
I'm now in my second season with a new pool build. Details are in my signature. I know early on, pH rise was expected with new plaster, and I also know SWGs add hydrogen off-gassing which increases pH. Now that I've fired the chlorinator up for the season and paying more attention to my pool, I am adding more acid than I expected. I just wanted to get an idea if I'm in the ballpark or not as I still feel I'm adding more acid than I expected to.

First, here's my chemistry break down from about a week ago, chlorine and pH are tested daily:

FC - 5
CC - 0
pH - 7.8 - 8.0
TA - 70
CH - 575
CYA - 70
Salt - 3600
Water Temp - ~70
CSI - -0.24
SWG run time right now is about 3.5-4 hours (6 hours pump at 60%), our weather and sun has been all over the place so this has been a moving target recently.

I'm playing with acid strategies, but I'm basically daily adding ~16 oz. of 31.45% MA to maintain what I can best tell is a daily 0.2 pH rise. It seems to be about the same whether I'm doing 8.0 -> 7.8 daily or 7.8 -> 7.6. It's worth noting, I'm dropping the acid directly into the deep end around where the main drains are. Due to the pool design, all my returns are on the infinity edge side and I only have access to one return on the shallow side near my swim up bar. I do stir up the water after acid delivery, and one of my water features runs for 10 minutes shortly after and spills over right into where I put the acid. Typically if I retest within an hour, I'll see lowered pH pretty well distributed at all corners of the pool.

Using the off season and some extended travel (SWG off) as reference, I feel like my pool likes to relatively quickly rise to 8.0 then still relatively quickly to 8.15 - 8.2 pH and can then quite slowly creep after that. I've never seen it go over that, but it's RARE I ever let it get that far. The few week long trips I've done, my neighbor will use my digital pH meter (well calibrated Apera AI1311) which seems consistent with my Taylor red drop test (so 4-5 days might be the longest I've gone without MA being added). If I recall on one of these trips, I left the house with the pool at 7.5 and then 5 days later my neighbor said the pH was 8.15, but I can't recall and that was in December.

So this basically puts me at a gallon per week of MA now, and I anticipate doubling SWG run times in Summer plus the added aeration of near daily swimming. I'd love to avoid having to do this daily, and last Summer I was at times doing 28 oz every other day and maintaining larger swings. I intended to add IntelliPh, but new guidance says it's not really compatible with an IC60, and I don't want to downgrade to a 40 as peak Summer uses a pretty high SWG %.

Finally, my water features only run 10 minutes a day just to keep things circulated.

I read of other people who add MA once a week (even with SWG+plaster), and I guess I was hoping for that now that the plaster has cured. I think one outstanding variable I have is a lot of pool surface area, and all of it is well above ground and gets way above average wind. We've had some windy days in the past month, but the last few haven't been so windy and it's more or less the same. That said, even when it's not windy, I live on a canyon that seemingly always has a gentle breeze and there's nothing to help block the pool from that (no trees, fences, buildings, etc).

Looking for sanity checks. If it's 4 gallons of MA a month in Summer for the rest of eternity, so be it, but I'd feel better knowing this is normal.
 
hmmm, If it were me I would drop the PH to 7/7.2 every time and a week later when it is at 7.8/8 drop it again.. not sure why you are only dropping it .2 unless you really want to do it every day... My TA is a little lower than yours but I have a vinyl liner so no issues but you may try it depending on your CSI :)

What is your CSI now?
 
CSI was reported there, -0.24 when pH was at 7.6, it goes to -0.040 at 7.8.

That also asnwers the question of why I don't go lower. At 7.2 or even 7.5 I start to fall out of the recommended CSI ranges. I don't have enough testing of the impact of pH to TA to say for certain, but using pool math, even if my TA comes down with pH my CSI falls out of range.
 
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Jimrahbe said:
DB,

Does your infinity edge run all the time the pump is on??

I'd let your TA drop to just above 50 and see if that helps..

Thanks,

Jim R.
Click to expand...

It's a faux/knife edge, no catch basin, no pumps no waterfall so that's not even a variable.

As I said above, I need to do a better job of testing TA changes between acid pours. I don't have a good handle on that relation. I did a full chem test last weekend after dropping acid in the morning so with a measured pH of 7.6 I think I recorded 60-70. I thought pH and TA rose and fell consistently with each other. I could acid the pool down to 7.2 to get TA to go down, but I imagine it'd creep back up with pH at the same rate? I probably need some education there, and as stated probably need to test TA at different pH levels. Can you educate here?
 
During this time of acid addition, if your TA is staying constant, then something is adding TA continuously which is a major factor in pushing your pH higher. Fill water is the most likely suspect. How much fill water are you adding?
 
Sorry, I missed your CSI number as you posted it :goodjob:

TA will only come down when you drop PH, it will not rise as the PH does... I think Marty hit it that your fill water is raising your TA, so what TA is your fill water?
 
My plaster pool is 4 yrs old, and I still routinely have to add acid. It's worse in the spring until I can get TA down -- just opened last week and TA was 100, had to add almost a gallon of MA. I typically run TA around 60-70 in the summer, but ph creeps up to 7.8-8.0 every 2-3 weeks anyway. I add acid to get it down to 7.2ish, lather, rinse, repeat. I think it's just some pools ... plus I have a waterfall which def raises ph.
 
Thanks team, I'll try to answer all the questions, and I just tested again.

pH - 7.56
TA - 60-70 (barely a change from drop 5 to 6 then no change from 6 to 7).

I was unaware that TA doesn't go up with pH, so maybe I should acid shock this thing down. Pool math suggests reducing acid to 7.0 - 7.2, so I can try 7.2 now and report back? Let me know if that's a good idea, I'm already at 7.56.

In regards to fill water, my auto-fill is shutoff and I manually fill through an RV water softener (since CH has been a concern and is a concern of other TFP'ers using City of Austin water). I did fill 500 gallons last weekend, but I'm not regularly filling so I don't think that accounts for the day over day increase, but it probably is the reason TA baseline is so high. I think I made the dumb mistake of assuming TA and pH were entirely linked.

Anyways, any alternative recommendations? Otherwise, sounds like going down to 7.2 and retesting TA is my course of action. Please advise.
 
shanebo said:
My plaster pool is 4 yrs old, and I still routinely have to add acid. It's worse in the spring until I can get TA down -- just opened last week and TA was 100, had to add almost a gallon of MA. I typically run TA around 60-70 in the summer, but ph creeps up to 7.8-8.0 every 2-3 weeks anyway. I add acid to get it down to 7.2ish, lather, rinse, repeat. I think it's just some pools ... plus I have a waterfall which def raises ph.
Click to expand...
Every 2-3 weeks for acid creep is like a dream state for me right now, haha.
 
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mknauss said:
During this time of acid addition, if your TA is staying constant, then something is adding TA continuously which is a major factor in pushing your pH higher. Fill water is the most likely suspect. How much fill water are you adding?
Click to expand...

TA of fill water is also 70. Maybe a little higher as the second to last drop was more pronounced than pool water.

Just found this which seems to say 70 for tap:
 
With a pool water TA of 60 and a CYA of 70, your carbonate alkalinity is all ready pretty low, so I would not press it lower with a large acid addition. Just let your pH get to 8 or even a touch higher, then lower your pH to 7.6. See if that helps stretch out the additions.

The other option is adding borates. It will not reduce the amount of acid added, just stretch out the time frame over when it needs adding.
 
mknauss said:
With a pool water TA of 60 and a CYA of 70, your carbonate alkalinity is all ready pretty low, so I would not press it lower with a large acid addition. Just let your pH get to 8 or even a touch higher, then lower your pH to 7.6. See if that helps stretch out the additions.

The other option is adding borates. It will not reduce the amount of acid added, just stretch out the time frame over when it needs adding.
Click to expand...
Too late, I put more acid in as I have a meeting starting right now. I've definitely have done 8.0 -> 7.6 routinely and that hasn't really help, I mean maybe I get an extra day as it'll go 7.6 to 7.8 the first day then to 8 by the next.

I'll report back on pH and TA in an hour or so.
 
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DB-Cooper said:
I'll report back on pH and TA in an hour or so.
Click to expand...
ok --- No harm.

When you test and see your pH is higher and you need to add acid, are you testing your TA? That is the time you need a TA value so you can enter it into Poolmath to get the proper amount of acid needed to lower your pH to target level.
 
mknauss said:
ok --- No harm.

When you test and see your pH is higher and you need to add acid, are you testing your TA? That is the time you need a TA value so you can enter it into Poolmath to get the proper amount of acid needed to lower your pH to target level.
Click to expand...
So I am using Pool Math and inputting 70 as my TA as that has been fairly stable through my testing, but I'm not testing them together regularly. It's possible I'm testing my pH and getting a high reading and using a lower TA since typically I test chems after I think I've got FC and pH relatively in line. Not sure if I'm making sense.

Have no fear, my pH will be up in no time. I'll test pH and TA again in an hour, report back, then I'll test tomorrow morning before any chemical additions and report, etc. That way we can all see how it relates. I also need to probably add 1,000 - 1,500 gallons tomorrow. The expected rain never came and I'm a bit low on water.
 
What’s the reaction time for the TA to go down. Just tested ph at 7.25 and TA is still 70, seems almost 60 but net down is no more than 10. Things aren’t fully circulated but the water is tested from the same area at the same time.

Hopefully my reagents aren’t bad.

This article and a few posts seem to indicate you can't immediately lower TA and it takes running pH lower for a longer period of time:
www.troublefreepool.com

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.
www.troublefreepool.com www.troublefreepool.com

I'll see where I end up tomorrow morning. I'll maybe try to drop pH daily to 7.4 or 7.5 and monitor TA.
 
Last edited:
DB-Cooper said:
What’s the reaction time for the TA to go down.
Click to expand...
When you add acid, it consumes alkalinity. That creates CO2 which makes the pH lower in the water. Then outgassing of the CO2 (from aeration, not the SWCG) makes the pH rise.
 

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