- Mar 5, 2020
- 2,967
- Pool Size
- 66000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Astral Viron V35
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?
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?
