Unexplained pH rise

xDom said:

I keep my TA at around 50 ppm and I keep my pH at about 7.7 to 8. I use 5 litres ( 1.3 gallons ) every two months in a 30 000 litre ( 7925 gallon ) pool. Do think this is normal usage?

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I use less acid than that and my pool is more than 3X as large. If you are aerating the water a lot that might explain the acid usage.

What brand SWG?

PoolStored said:

After you get your TA down, stop lowering your pH to the low 7s as you are doing. Lower pH causes more rapid pH rise.

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^^^ This!

I battled pH rise. I kept trying to force it down. The more acid I used to do that, the more acid I needed to use to do that! And it seemed to be exponential. Going from 7.8 to 7.7 takes a lot less acid than going from 7.3 to 7.2.

I learned to let it come up a bit, and saw my acid consumption plummet.

I later installed an acid dispensing system and that was the end of hassling with pH and acid. My new plaster never ended up using much less acid. Five years later and I still use a good amount (though not a gallon a week!). I expect it is my fill water TA that is driving acid consumption.

If you go with automation, I’d recommend a “dumb” system, one that doesn’t also try to measure pH and dose automatically. Once I got the settings right, I test pH once a week and it’s always fine. I’m glad I don’t have to deal with a pH probe, keeping it calibrated, and worrying if it’s working or not. And that’s the rub, even with a fully automated system you still have to test manually once a week to confirm it’s working. Well I test once a week! So why would I need a complicated pH measuring probe and computer??

You’re getting good advice above, just follow it. Even your own. You mentioned you are spiking big acid doses. I presume that is to minimize how often you have to dose. I think you’re right, that practice is contributing to the high acid consumption. The nice thing about my automation is that it doses a small amount every hour. My pH is rock solid steady all the time. No big pH highs and lows, which lowers consumption and makes swimming more comfortable for me (my skin does not do well with large pH swings).

In some cases, plaster dissolves and causes the pH, TA and CH to rise.

If the pH rise is due to plaster dissolving, then the TA and CH will rise by the same amount.

Are the TA and CH rising at the same rate?

What is the pH being kept at?

At what pH is acid added?

What are all of the readings?

What is the CSI range?

Track CH and TA to see if they gain the same amount over time.

If the CH is rising with no calcium being added, then it might be coming from the plaster.

JamesW said:

If the CH is rising with no calcium being added, then it might be coming from the plaster.

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Note that there can be CH in the fill water, and depending on where you live, it can be a substantial amount. Easy to measure with your kit.

xDom said:

So how much would you use in a say, a week?

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Short version: dunno.

I suppose I should/could figure that out, but I don't actually know. My IntellipH calculates the hourly dose based on a user-adjustable setting. But that setting is 0-100, so it's not in ounces of acid. (Because the IpH controller doesn't know what percentage of acid is in its hopper.)

I've never bothered to figure it out because it doesn't really matter for my MO. I adjust the 0-100 based on the pH level in the pool, and I base what pH I want in the pool based on CSI, which fluctuates throughout the year (primarily because of water temperature). If it helps, I run about pH7.5 in the heat of summer, and about 8.0+ in the dead of winter.

I load up the IpH with 31% muriatic diluted 1:1 with water. It seems I've barely used any this winter, and maybe go though about five or six gallons a year total. Again, I don't really keep track. My pool tells me what to do, and I just do it!

I've been tempted to pull the injector to measure exactly how much acid it dispenses per minute, but I'd question the result. One, I change the setting throughout the year, and two, I'm not sure the amount I'd measure would be the same as when the injector is in place, because of the back-pressure of the water in the plumbing. And since the actual amount dispensed would still have no bearing on my MO, I've just never been inspired enough to find out.

I think the manual indicates the dispensing rate, but, again, because my rate changes throughout the year, it would be quite a task to figure it all out, and even if I did it would be of no use to me.

More to the point, acid consumption is based on a handful of factors, primarily what your plaster is doing, the pool's annual average water temp and the chemistry of your fill water. So even if I could give you a number, unless you lived next-door with a pool that had a size, shape and finish exactly like mine, installed when mine was, it wouldn't tell you anything useful.

+1 to modest doses. Used to be that when mine hit 8.0 I'd dose to get it all the way back to 7.3-7.4. In mid-summer, a day or two would take it back to 7.6, then it would take 8-10 days to get back to 8.0. Gradually I figured out there is a sweet spot for (days between adds) / (amount of acid). So currently I seldom if ever go below 7.6.

Also, I'm thinking if I ever do automate, I'll just add a Stenner, where I can press a button in my app and have it deliver a standard dose. No sensor. If I had a sensor I'd still be out there with the Taylor test anyway to make sure the sensor is accurate.

xDom said:

I keep my TA at around 50 ppm and I keep my pH at about 7.7 to 8. I use 5 litres ( 1.3 gallons ) every two months in a 30 000 litre ( 7925 gallon ) pool. Do think this is normal usage?

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What's interesting about this is that by adding 5 L of MA, you are compensating for a TA rise of 80ppm in that two month period. That seems quite much

I think it would be best to start your own thread, and give a few more details, including your fill water parameters and how much evaporation you have to replace.

Or are you adding bicarb?

"Bicarb" can arrive in the form of various pool products known as: Buffer; pH Buffer, Alkalinity Increaser; Alkalinity Up; or the commonly used chemical, sodium bicarbonate aka baking soda

FWIW because pool and fill water varies, I do four pools and experience a range of 1 quart/~litre to 1.5 gallon (6ish litres) per pool per year. The one that uses a lot has younger plaster. Our fill water TA is relatively low here in Sydney, around 30 ppm TA. In a dry year I use more acid. I keep pH 7.8 to 8.0 most of the time.

Just find your case interesting, thought it'd be worth trying understanding what's going on.

The amount of added acid is directly proportional to the TA-reduction caused by the acid (calculating the TA-effect is much easier than the pH-effect), and 5 L of MA in a 30000L pool cause a TA reduction of about 80ppm. If your TA remains constant through all this without any bicarb additions, then there is another effect going on that causes a TA-rise. CO2-outgassing is TA-neutral and only causes pH to rise, but at TA 50, pH should be pretty stable in that higher range.

The most common causes for TA-rise are fill water additions to replace evaporation. That's why I was interested in your fill water TA.

The other common culprit is plaster dissolving due to bad water chemistry, but you have a FG pool, so that's ruled out.

As I said just curious. If you want us to look into it, then I'd start with testing your fill water TA and with an estimation how much evaporation you typically have to compensate.

But absolutely fine if we let those geese fly. No pressure

xDom said:

When I see the pH has risen to 8 I get a bucket of pool water and manually pour some acid into the bucket, then throw it into the pool.

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It may be that you are just over dosing your pool.

Maybe let it get to 8.2, then only add enough to lower it to 7.8 or 7.9. Rinse repeat.

You may find your usage goes down.

Do you ever use baking soda?

What is the TA and CH of the fill water?

Does the CH go up over time?

How much evaporation do you get?

xDom said:

My gut feeling is this is the issue. I've rigged up a system when I can get an exact quantity, I'm gonna see how this plays out.

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Mine too.

xDom said:

So my range has been between 7.7-8.0. You don't see an issue taking that range up to 7.8-8.2 ? As a permanent change?

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Nope. Yep.

xDom said:

I'm sure I would use less acid, I just thought the TFP way was to keep pH in the 7's.

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7.9 is in the 7s. With TA of 50...you may find it sits at 8. When it gets above 8, unless you are using a calibrated meter, you don't know what it is...when it gets darker than 8, bring it down slowly (.1 increments) to 7.8 or 7.9, so you don't overshoot.

How far is the SWG cell from the return?

The SWG might be the cause of some, or all, of the pH and TA rise, but we don't have any hard evidence or logic for how that would happen.

If you get a lot more specific details that you can post, we will try to help you as much as possible.

Maybe pictures of everything would help.

PoolStored said:

….When it gets above 8, unless you are using a calibrated meter, you don't know what it is...when it gets darker than 8, bring it down slowly (.1 increments) to 7.8 or 7.9, so you don't overshoot.

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For my 9 month old plaster pool I ended up buying a calibrated meter that i keep calibrated and check with standards and I don’t adjust my acid until the pH gets to 8.6 then I add 1.25 cups acid to take it down to 7.8 (about 11000 gallons in its current winterized state) which lasts for 6 days until its back up to 8.6 again. The reason I let it go so high is because 8.6 is where the csi goes above 0.6 so I adjust back down to Csi of -0.25 and have been running this cycle for the last month while the water temperature is in the 30’s........... yep

Dirk said:

My new plaster never ended up using much less acid. Five years later and I still use a good amount.....

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five years later?!?
My pool is 9 months old and I was told 10 months to 1 year to fully cure and stop needing to make such frequent acid additions... You just told me there is no santa claus.....