Trouble with pH and TA in salt pool

[Russmd]

I have an in-ground 40,000 gal salt-water pool with a waterfall which is always flowing when the pump is on. The water source in our area is hard and I have a softener on it which improves the TDS situation to a degree, but if I let the pH go even a bit over 7.8, I start to get scale on the tiles and cell. I just had the pool RO’d so the TDS is currently low. The problem is that it needs 1/2 to 3/4 gal of acid a week just to even keep it below 8.0, and that quickly drives the TA down. Last week, I got the pH to stabilize a little better at 7.8 but found the TA down at 40. I added just a little bicarb getting the TA to 70 and pH -boom- back up to 8.0. I have 50 ppm borates in already. As I said, I can’t turn off the waterfall in this system as it is part of the main pump flow which goes through the spa.
Any thoughts as to how I could try to keep my pH 7.6-7.8 without always driving the TA too low? I read many saying that in a salt pool, TA of 60 is ok but even there, my pH rises to 8.0 within a week.
Ideas?
Thanks,
Russ

 

[mas985]

Post a full set of test results for the pool

Also, post the fill water CH, TA, PH

CSI is the most important reading to determine the probability of scale and one can't look at just any one or two components of CSI as they are all important.

We also have very high CH, TA, PH fill water which means with evaporation, everything has an upward trajectory. This is why I installed an acid dosing system. This helps keep CSI fairly stable (-0.3 target) but it also means that when CH gets really high, TA tends to get really low which I never had any issue with.

 

[Russmd]

Post a full set of test results for the pool

Also, post the fill water CH, TA, PH

CSI is the most important reading to determine the probability of scale and one can't look at just any one or two components of CSI as they are all important.

We also have very high CH, TA, PH fill water which means with evaporation, everything has an upward trajectory. This is why I installed an acid dosing system. This helps keep CSI fairly stable (-0.3 target) but it also means that when CH gets really high, TA tends to get really low which I never had any issue with.

Pool:
Full 5.0
PH 8.0
TA 70 (was 7.6, TA 40 a few days ago before I added about 8lbs bicarb)
Cya 50
Borates 50
CH 350

Fill:
7.4
CH <50 (softened)
TA very low <20

 

[mas985]

Pool:
Full 5.0
PH 8.0
TA 70 (was 7.6, TA 40 a few days ago before I added about 8lbs bicarb)
Cya 50
Borates 50
CH 350

Fill:
7.4
CH <50 (softened)
TA very low <20

Your current CSI is a little high, 0.06. I would target a CSI -0.3 or a PH of 7.7.

I think you have been targeting too low of a PH value instead of focusing on CSI which is really what matters for scaling.

If TA drops a little too far after dosing, don't worry, nothing horrible is going to happen. During the lifetime of my pool, the TA has dipped down to 40 several times. Plaster is in it's 19th year so no worries. Low TA just allows PH to move a bit faster and allow for a little higher PH values to maintain CSI.

 

[mknauss]

Very odd to have high CH well water (that you run through a softener) that has low TA. The softener does not effect TA.

 

[Russmd]

Your current CSI is a little high, 0.06. I would target a CSI -0.3 or a PH of 7.7.

I think you have been targeting too low of a PH value instead of focusing on CSI which is really what matters for scaling.

If TA drops a little too far after dosing, don't worry, nothing horrible is going to happen. During the lifetime of my pool, the TA has dipped down to 40 several times. Plaster is in it's 19th year so no worries. Low TA just allows PH to move a bit faster and allow for a little higher PH values to maintain CSI.

Thanks. So with my numbers above, when it was 7.6 and a TA of 40, do you think I shouldn’t have added any bicarb? You see that as soon as I did, things jumped up quite a bit.

 

[mas985]

I probably would not have added bicarbonate.

When targeting CSI or PH, you are better off doing half what you think you need so you don't overshoot.