extreme TA drop, is this even possible?

mgtfp

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Mar 5, 2020
437
Melbourne, Australia
I don't have too much experience when scaling really becomes an issue, I have very soft water and am usually more on the other end of the CSI spectrum, trying to keep my water from not becoming corrosive to my plaster, especially during winter. Ideally, you should keep your CSI between -0.3 and +0.3. You won't have a problem at the lower end with your CH.

With your current parameters (assuming 90°F water temperature and salt at 3500ppm), your CSI will reach 0.3 between pH 7.6 and 7.7. At pH 7.8, your CSI will be 0.43, I don't think that will create an instant problem. The CSI interpretation is usually that above 0.3 there is a scaling potential, and above 0.6 it will quite certainly create scaling.

The first location where scaling occurs is often in the SWG cell. That can create flakes that will come out of the return jets. If you see calcium quickly building up in your cell, and/or flakes coming out of the return jets, then you should aim for a lower pH. But if you force it too low, it will probably move up too quickly again (more CO2 out-gassing at lower pH), and you end up in this cycle of adding muriatic acid, then adding baking soda again to bring up TA, which will increase the pH-rising rate again.

I have the impression, if you maintained your TA between 50 and 60, you should be fine with the pH going up to 7.8 before you bring it down again. With your initial numbers of TA around 100, I thought, a lower pH would be required, but TA 60 is quite good - that's where reliable test results are important :)

Once you reach pH 7.8., I'd add about 10oz of muriatic acid, that should bring pH down to about 7.4 and TA to about 55 (but use PoolMath to confirm the effects based on current test results before you add anything). See how you go from there. Once TA gets below 50, you can start thinking about adding some baking soda. But see how your pool reacts. If your pool finds a sweet spot at TA 40 with stable-ish pH, then I wouldn't force the TA back up with high CH levels like yours.

Watch your CH, if that rises further, the you might have to adjust your pH/TA levels accordingly. Just keep calculating CSI with PoolMath and make sure it doesn't get too far above 0.3, certainly not above 0.6. Should your water temperature get into the hundreds, then you really don't want your pH above 7.8.

If you are scared of scaling you can try a lower pH limit before you correct. But aiming for lower pH often ends up in pH rising back up very quickly.

You will probably have to add some CYA. When doing that, then remember that CYA is also an acid, so I would do that at a time when you want to bring your pH down again. You then just CYA instead of muriatic acid, which will bring down pH. The "Effects" section of PoolMath will tell you how much. In your case, adding enough CYA to bring it up to 80, will lower your pH probably from 7.8 to 7.3. You don't want to add muriatic acid at the same time.

But all of this is just based on my theoretical understanding of the CSI, I don't have real life experience with high CH levels (apart from when I lived in Europe, where I had to deal with scaling in my water kettle on a weekly basis, but I didn't have a pool to look after there...).

Maybe @mknauss will have advice based on more experience?
 
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mknauss

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May 3, 2014
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Laughlin, NV
To be honest, if the CH of 1225 ppm is anywhere near correct, I would be doing a complete water exchange. I do mine once I reach 800 ppm. It just becomes really difficult with high TA fill water to keep the TA and pH low enough to keep from scaling in the SWCG.

Be sure you are doing the Fading Endpoint method of CH test. See Calcium Hardness - Trouble Free Pool
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
With your current parameters (assuming 90°F water temperature and salt at 3500ppm), your CSI will reach 0.3 between pH 7.6 and 7.7. At pH 7.8, your CSI will be 0.43, I don't think that will create an instant problem. The CSI interpretation is usually that above 0.3 there is a scaling potential, and above 0.6 it will quite certainly create scaling.
my water is only at about 78 right now (according to the waterguru), not sure how much that will substantively change the CSI calculation since i don't know the actual formula.

You will probably have to add some CYA. When doing that, then remember that CYA is also an acid, so I would do that at a time when you want to bring your pH down again. You then just CYA instead of muriatic acid, which will bring down pH. The "Effects" section of PoolMath will tell you how much. In your case, adding enough CYA to bring it up to 80, will lower your pH probably from 7.8 to 7.3. You don't want to add muriatic acid at the same time.
is there any harm to using the liquid stabilizer rather than the granules, aside from cost? i remember using the liquid stuff a few years ago before i gave up trying to manage this on my own, it seemed like a much easier way to get CYA into the water than the granules...

To be honest, if the CH of 1225 ppm is anywhere near correct, I would be doing a complete water exchange. I do mine once I reach 800 ppm. It just becomes really difficult with high TA fill water to keep the TA and pH low enough to keep from scaling in the SWCG.
i'm probably going to have to do at least a partial water exchange coming up when i have the rocks stripped and repainted to remove the scale that has already appeared along the water line...am i hurting anything by just waiting until that point to do the water swap instead of having to do it twice?

i haven't tested the fill water yet, i plan to do that tomorrow when i do my weekly maintenance.
 
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mgtfp

Bronze Supporter
Mar 5, 2020
437
Melbourne, Australia
my water is only at about 78 right now (according to the waterguru), not sure how much that will substantively change the CSI calculation since i don't know the actual formula.
Colder water will work in your favour. You don't need to know the formula, just put your water parameters into PoolMath. At the bottom of the TFP website is a link to the website version of PoolMath, very simple to use.

is there any harm to using the liquid stabilizer rather than the granules, aside from cost? i remember using the liquid stuff a few years ago before i gave up trying to manage this on my own, it seemed like a much easier way to get CYA into the water than the granules...
I don't think so. As you said, usually more expensive. And I heard that the sludge at the bottom of the bottle is quite hard to get out, requires thorough rinsing with pool water, only really possible when you have to top up enough to use the full bottle. I heard of people who wanted to use only half the bottle, but couldn't get the dosage right because most of the CYA had settled to the bottom of the bottle, and even vigorous shaking didn't get it evenly dissolved in the bottle.
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
@mgtfp and @mknauss

two interesting bits from my maintenance and testing today:

1) my pool CH test was accurate, or at least pretty close. i did it again today and got 1150 (45 drops)...so not quite as high as the other day, but the same general area.

2) my fill water is surprisingly NOT that hard and very high alkalinity...

FC 3 (somewhere between 2-3, my wife and i both were having a hard time figuring out which color yellow to use)
pH 8.2
TA 170
CH 150
 

mknauss

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May 3, 2014
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Laughlin, NV
It took many years for your CH to reach its current level with that fill water. Or, someone used a lot of calcium hypochlorite 'shock' in the past.
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
It took many years for your CH to reach its current level with that fill water. Or, someone used a lot of calcium hypochlorite 'shock' in the past.
since i'm going to have to do at least a partial water exchange when i get the rocks redone, is there any harm to leaving it as is for now until that time? will hopefully (probably) be later this summer...
 

mknauss

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Scale is the only issue. Especially in the SWCG. If it starts to throw off calcium flakes, your CSI is too high and you need to lower pH or TA or both. Also start to look for scale occurring below the water line. That at the water line and in your rocks is normal and will always occur in our climate.
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
Scale is the only issue. Especially in the SWCG. If it starts to throw off calcium flakes, your CSI is too high and you need to lower pH or TA or both. Also start to look for scale occurring below the water line. That at the water line and in your rocks is normal and will always occur in our climate.
any suggestions for what to look for when getting bids on the rocks repainting to minimize the scale or potential for having to get them repainted again too soon? i'd like to have it last longer than the 5 or so years we've gotten out of this initial set if possible...i've looked into whether or not they can do a sealant on them, some of the people i've talked to have said they can and others have said they don't recommend it.
 

mknauss

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May 3, 2014
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Laughlin, NV
You will get evaporite scale on any surface that gets splash or is an active waterline. Just the way it goes. Those type of water features look nice when new.
 

mgtfp

Bronze Supporter
Mar 5, 2020
437
Melbourne, Australia
Good to see that your testing is consistent now. A reliable test kit makes a bit difference :)

Interesting to see how different fill water can be. It's not just H2O... First, I was surprised to see FC and pH so high (my water usually has FC below 0.5 and pH around 7.6). But then I looked up the guidelines and found out that in Australia drinking water is allowed to have up to 5ppm FC and pH between 6.5 and 9.2. In the US, the EPA seems to specify FC up to 4 ppm and pH between 6.5 and 8.5.
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
You will get evaporite scale on any surface that gets splash or is an active waterline. Just the way it goes. Those type of water features look nice when new.
that's what i was afraid of. i had considered getting a complete overhaul done and having the faux rocks ripped out in favor of a more traditional deck, but i'm not sure that's in my budget right now.
 

mgtfp

Bronze Supporter
Mar 5, 2020
437
Melbourne, Australia
I guess the only way to minimise evaporative scaling is to minimise CH in your water, managing CSI can't fix that completely. Once water from a puddle on your rocks evaporates, the Ca will remain there.

After your drain/refill your CH will probably be OK for a while, but depending on how much evaporation needs to get replaced with tap water, it will rise again. You should probably consider replacing some water each year, rather than having CH gradually creeping up until you see scaling again and are forced to do another (more or less) complete water exchange.
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
so, interesting data point from the past few days: my pH has been pretty much stable since saturday, and actually drifted down 0.1 today. last time i added acid was last tuesday (so 9 days ago), and that was an overshoot that brought the ph down to 7.1 (based on what the waterguru reported, since i didn't yet have my TF-100 at that time).

here's the journey over the past week (friday was my first day with the TF-100 in hand):

friday: waterguru 7.3, TF-100 7.2
saturday: WG 7.5, no TF-100 test
sunday: WG 7.5, no TF-100 test
monday: WG 7.6, no TF-100 test
tuesday: 7.7 WG, no TF-100 test
wednesday: 7.7 WG, 7.5 TF-100
today: 7.6 WG, 7.5 TF-100

does this mean my pool is actually stable and balanced, or should i be worried that something else is wrong? this is the first time i've seen pH drift down, including the very brief period years ago when i tried to do this myself before hiring someone else to do it...
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
You only show one test from the K1000.

Whoops - I see the one for today -- it is back to 7.5. No issues.
there are 3 there, it just might be formatted weird. there are pH numbers there from the past two days and the first day i had the kit in hand.

edit: nevermind, i just saw your edit. does that mean i'm pretty much balanced now or should i still be keeping an eye on something? basically i'm trying to figure out if it's normal for the ph to drift around like this (although according to the TF-100 it's the same, the WG i guess is reading at a higher precision)
 

crackers8199

Well-known member
Jun 5, 2014
119
Lake Elsinore, CA
OK -- so I do not see an issue. Your pH is in the 7's. All good.
just wanted to make sure of two things basically:

1) is it normal for the pH to drift downwards (if in fact the waterguru is measuring at a higher precision than the TF-100 does)?

and 2) does this mean i want to keep TA right around 60 to keep the acid demand as low as possible?

and, by extension 3) if yes, next time i need acid to bring the pH down do i want to also then add baking soda to push the TA back up?