My first acid addition: Sanity check

[ChrisA76]

So today I tested my (perfectly clear) water and got:
FC: 6.8
CC: < 0.5
pH: > 8.0
TA: 120
CH: 320
CYA: Just about 30*

The pH was obviously concerning, so my further thoughts about it are as follows:

1. For the whole last month my CH was consistently ~350 on my Taylor kit *and* at the pool store. My thinking is that this drop due to the water getting near the scale forming range and therefore it's slowly shedding some Calcium onto the plaster or tile or elsewhere. I don't see any scale but maybe it's not visible yet.
2. I did an acid demand test and 2 drops brought me down to about 7.6 pH. 1 drop still looked like roughly ~8.0.
3. It seems pretty clear that I need to add Muriatic acid, maybe without bicarb since I clearly need to lower my pH and I am going to be totally fine lowering my TA down to the 90 range anyway.
4. Should I add the acid equivalent of 2 drops worth (amount via PoolMath) and retest or just go for the equivalent of 2 drops worth since I'll still likely be at a good TA even after 2 drops worth.

* = I can just barely not see the dot at the 30 ppm line and this makes sense from the amount of CYA I added 3 days ago when I opted to bring this up from 20 ppm to about 30 ppm according to a pool store measurment last week. Please no flaming about the pool store measurement, I'm quickly transitioning to doing all my own testing.

EDIT: Looks like CSI is about 0.41 so getting on the high range and I clearly need to take some action.

Am I on the right track? What am I missing?

 

[ajw22]

CH of 350 is no where near scaling range. CH up towards 800 is manageable.

Turn on CSI Tracking in PoolMath and calculate your CSI. Your CSI predicts your danger of scaling.

Calcium Saturation Index (CSI)

How is CSI calculated? Very simple – use our PoolMath tool. To ensure long plaster life and save money, click here to learn more.

www.troublefreepool.com

Lower your pH using MA. Use PoolMath to calculate the dose. If pH is above 8 tell PoolMath it is 8.2 for the calculation with a target of 7.6. Add the MA and wait 30 minutes and retest. If pH is still above 8 then repeat until you have a pH into the 7's.

TA down to 60 is fine. Let your TA find an equilibrium with your pH. Don't yo-yo your pH and TA with bicarb.

Have you read Pool School?

Pool Care Basics Archives

Your one-stop shop for all things TFP to include: ABCs of Water Chemistry, Recommended Chemicals/Levels, Test Kits, Troubleshooting, and much more!

www.troublefreepool.com

TA - Further Reading

www.troublefreepool.com

PH - Further Reading

www.troublefreepool.com

PH TA Relationship - Further Reading

www.troublefreepool.com

 

[ChrisA76]

CH of 350 is no where near scaling range. CH up towards 800 is manageable.

I thought scale forming was from a combination of levels and that's what CSI is for. I've never seen a claim that only CH matters is scale formation.

Lower your pH using MA. Use PoolMath to calculate the dose. If pH is above 8 tell PoolMath it is 8.2 for the calculation with a target of 7.6. Add the MA and wait 30 minutes and retest. If pH is still above 8 then repeat until you have a pH into the 7's.

Makes sense.

TA down to 60 is fine. Let your TA find an equilibrium with your pH. Don;t yo-you your pH and TA with bicarb.

Great, this makes sense.

Have you read Pool School?

Not in entirety, I'm still going through all the articles. Thanks for the links.

 

[ajw22]

For the whole last month my CH was consistently ~350 on my Taylor kit *and* at the pool store. My thinking is that this drop due to the water getting near the scale forming range and therefore it's slowly shedding some Calcium onto the plaster or tile or elsewhere. I don't see any scale but maybe it's not visible yet.

Your thinking there is incorrect.

A CH difference between 320 and 350 is not a big deal. Move on from that.

EDIT: Looks like CSI is about 0.41 so getting on the high range and I clearly need to take some action.

Just get your pH back into the 7's and your CSI will come down.

 

[Newdude]

Please no flaming about the pool store measurement, I'm quickly transitioning to doing all my own testing.

Here's the skinny. You are officially the smartest person in the class. Do not cheat off the dumbest person in the class (named Leslie). I don't give a flying hoot if Leslie got it right, or even close last time. Each time is a high probability he'll be wrong again. You have the answer key in your pocket. Trust it.

To help set your mind at ease, you can be off a little on the tests and it's of no consequence because they're still right enough for what we do. A 325 or 375 CH for example, or a 7.8 / 8 PH. You're in the right ballpark. No harm will come in the short term before you test again. Leslie might as well have a random number generator and we have zero clue if it's even the right ballpark.

 

[ChrisA76]

Here's the skinny. You are officially the smartest person in the class. Do not cheat off the dumbest person in the class (named Leslie). I don't give a flying hoot if Leslie got it right, or even close last time. Each time is a high probability he'll be wrong again. You have the answer key in your pocket. Trust it.

To help set your mind at ease, you can be off a little on the tests and it's of no consequence because they're still right enough for what we do. A 325 or 375 CH for example, or a 7.8 / 8 PH. You're in the right ballpark. No harm will come in the short term before you test again. Leslie might as well have a random number generator and we have zero clue if it's even the right ballpark.

And here I was hoping to avoid a lecture about using pool store measurements by stating: "Please no flaming about the pool store measurement"

 

[Newdude]

here I was hoping to avoid a lecture

It wasn't a lecture. It was a pep talk. You got this

 

[ChrisA76]

And here I was hoping to avoid a lecture about using pool store measurements by stating: "Please no flaming about the pool store measurement"

FYI all the above measurements were my own except for the historical 350 CH which corroborated my own historical 350 CH measurements from my Taylor test kit. But you can be sure that this is the last time I'm going to mention any Leslie's measurement at all.

 

[ChrisA76]

Your thinking there is incorrect.

A CH difference between 320 and 350 is not a big deal. Move on from that.



Just get your pH back into the 7's and your CSI will come down.

I didn't mean to imply that 350 to 320 was a big deal. I didn't see scaling happen and my LSI was still ~0.35 or so. I was just being interested and curious. I'd never seen CH drop at all before after a month of testing and now I suddenly see it when LSI is higher.

 

[Newdude]

I was just being interested and curious

Remember that the tests have an accepted variance and also a human variance from trying to make 14 perfect drops. The test may have been off by 5% (negligible) and you another 5% (still negligible) and it's still plenty close enough for government work.

With CH, salt, CYA and TA you aren't going to change much week over week. You're really just looking for how it trends. You have a good start point of a change now. Maybe next time is back to normal. Maybe the trend continues and tips you off to a leak.

 

[aussieta]

if you are planning to add stabilizer
keep in mind 1lb of stabilizer will drop ph by around 0.2

 

[ChrisA76]

if you are planning to add stabilizer
keep in mind 1lb of stabilizer will drop ph by around 0.2

I’m going to stay where I am for now and potentially gradually increase it as needed later. But thanks for this

 

[mgtfp]

I thought scale forming was from a combination of levels and that's what CSI is for. I've never seen a claim that only CH matters is scale formation.

What he meant was that with CH 350, CSI is easily manageable.

CSI might sometimes get above 0.3 when TA crept up over time with fill water which as a consequence also will bring pH above 8 quickly. But as long as someone is testing regularly and corrects a situation like that, those trips into high CSI will remain short term and not cause problems.

Once CH is above about 800 on the other hand, pH will be required to be maintained in the low seven range to keep CSI low which will be a battle hard to stay on top off because of faster CO2 outgassing at these lower pHs. As a consequence, CSI will stay above 0.3 or even 0.6 for longer periods, resulting in scaling, eventually.

 

[ajw22]

You are not in scaling range until CSI exceeds +0.6 for a few months.

 

[ChrisA76]

So I added enough MA to bring it to the following:
pH: 7.6
TA: 120 (didn't measurably move, but after some brief reading on TA and pH moves from adding MA, this makes sense.)

Thanks to all who helped, @ajw22 @Newdude @mgtfp

 

[AUSpool]

You’ll barely notice any change in TA from a small acid addition. (Lots of small changes, yes, but not from any individual small addition). You can kind of get a rough idea of what to expect from using the “Effects of adding chemicals” feature down the bottom of the PoolMath page. When actively trying to reduce TA I add enough acid to reduce my pH from ~8 to ~7 which will reduce my TA by about 10ppm but even that is very close to the tolerance of the test.

I would suggest the low resolution option for the CH test. 1 drop = 25ppm is really close enough for own purposes and it will save on a reagent use.

As for point 1. There is no way that you can account for a 30ppm CH change due to scale formation, in a 14.4K pool that would be the equivalent of 64oz of calcium chloride. Testing variation would be the most probable answer. It would have to be a substantial leak to cause that change, enough that you would have other indications of a leak.

Forget about the acid demand test, thats old school, its way easier just to use PoolMath. Although the acid demand reagent is a good way to get used to the pH comparator colour changes.

In the words of Jimrahbe, pool management is more like a game of grenades rather then a game of darts, in that we don’t need to be super acurite. I don’t really bother to re test after an addition. I calculate my additions from PoolMath, double check my additions and record my test result, addition, and theoretically result after the addition. Any discrepancy will be picked up at the next test but you kind of get used to how much your pool needs.

 

[ChrisA76]

Forget about the acid demand test, thats old school, its way easier just to use PoolMath. Although the acid demand reagent is a good way to get used to the pH comparator colour changes.

Good point. The main reason I did the acid demand test was because I was reading higher than 8.0 pH. Is there a better way to do this?

 

[PoolStored]

Please no flaming about the pool store measurement

oooooh, oooooh, I got this. Stay out of the pool store and you will avoid being pool stored.

 

[PoolStored]

Is there a better way to do this?

Easy. Add enough MA to reduce pH from 8.0 to 7.2 and retest. At some point it will be under 8 and you can do final adjustment.

 

[AUSpool]

Is there a better way to do this?

Easy. Add enough MA to reduce pH from 8.0 to 7.2 and retest. At some point it will be under 8 and you can do final adjustment.

Same, and thats what ajw22 suggested in post #2. But be aware that pools are constantly in a state of change to some degree so be prepared to find that actual results don’t exactly match your predicted result. On occasion when I’ve dosed acid, tested, re dosed and tested again I’ve always found that the pH rebounds quite rapidly the first time but slower the second. But observations on my pool will differ from another.

Am I on the right track? What am I missing?

Yeh, I think your all over it. Getting to know your pool, asking questions. If your missing anything you’ll soon fill in the gaps.