Lowering Total Alkalinity; Is SWG use hampering the process?

[drichitt]

I would like to lower my TA from 100 down to 80. I have lowered the PH to 7.2 and set-up a single fountain to aerate as best I can. It has been about a week now with minimal movement in the TA reading (Initailly 105). I have had to add 6-13oz of muriatic acid every 2-3 days to keep PH at 7.2. I read in my Jandy Aqua Pure (SWG) manual that the SWG will buffer PH to maintain approx 7.6.

I didn't figure it would not be that big a deal to drop it 25 ppm.

My question is.... Is the continued use of a SWG advisable during the TA lowering process (add acid & aerate)? An excellent article here on TFP indicated that a SWG assists with the aeration process, so I am hesitant to stop the SWG. I feel I am basically adding acid to counteract what the SWG is producing.

I am considering lowering my temporary PH goal to 7.0 and adding a couple more aeration devices I saw referenced (pictured) in the TFP article mentioned above. But before I do that I thought maybe it best to check with those more knowledgeable on the subject.

FC=4.5-5.0
CC=0.0
PH=7.2
TA=100
CH=490
CYA=70
Salt=3400
Temp Fluctuating between 80-85

 

[mknauss]

Let your pH rise to 7.8 or 8. Then add the MA to lower it to 7.2. Use the Effects of Adding Chemicals in PoolMath to see what the TA drop is each time.

There is no real reason to force the TA lower. It will lower over time as you add MA to maintain your pH so that your CSI stays between -0.3 and 0.

 

[drichitt]

Let your pH rise to 7.8 or 8. Then add the MA to lower it to 7.2. Use the Effects of Adding Chemicals in PoolMath to see what the TA drop is each time.

There is no real reason to force the TA lower. It will lower over time as you add MA to maintain your pH so that your CSI stays between -0.3 and 0.

Thanks.... I will try what you suggest. My original goal was for CH to be 400 and TA to be 80. I slowly approached those targets. Once attained, they stayed there for awhile. Then for some unknown reason the CH rose to 490 and TA became 105 but seem to have now stabilized. I have not added any water in the past 2-3 months (rains have kept pool full). I live in the Fla Keys keeping the pool mostly covered and heated right now. My tap water tests 90 for CH and I am not sure about TA. My CSI goal is as you suggest; -.3 to 0. With my TA at 100 the CSI calculates to be -.25; with TA at 80 CSI should be about 0.0.

 

[Texas Splash]

Then for some unknown reason the CH rose to 490

That's interesting in that the CH should not increase unless you added calcium or a cal-hypo product. But you have an SWG so I would assume no CH was added. Possibly a testing variance? That's 2-3 drops I suppose. In either case, you're being proactive and that's good. Using the Poolmath tool and monitoring your CSI is good practice. Try not to get too wrapped around a specific number here or there, but watch the overall picture and CSI. You'll be fine.

 

[AUSpool]

There’s no reason to turn your SWG off while lowering the TA. There is always TA and CH in town water which is used for top ups and will slowly drive your TA and CH up. But up by 90ppm is a fair bit. I would advise testing your CH again and test your town supply for TA, CH and pH.

If you plot your theoretical CSI from poolmath, as your pH rises your CSI will rise to 0.27 as it reaches a pH of 7.8. Dont worry. Dose your pH down to 7.2, your TA will come down by about 10ppm and CSI will come down to -0.36. This time don’t worry about a slightly low CSI, it will start to come up with the pH. Repeat and repeat. Eventually at a pH of 7.8 and a TA of 70ppm you CSI will be at 0.04 which is a tad high. Going down again to a TA of 60ppm will get your CSI at -0.06 at a pH of 7.8. It would be nice to know now where your pH would like to settle without the extra airation.

The trick now will be to monitor your CH, if it continues to rise you will have to either lower your CH or maintain a lower pH.

 

[AUSpool]

My question is.... Is the continued use of a SWG advisable during the TA lowering process (add acid & aerate)? An excellent article here on TFP indicated that a SWG assists with the aeration process, so I am hesitant to stop the SWG. I feel I am basically adding acid to counteract what the SWG is producing.

To answer this again, a SWG will not hamper the acid/airation TA lowering process, most defiantly leave the SWG ‘ON’. It encourages your pH to rise. As noted before your pH must go from 7.8 to 7.2 with a larger dose of acid for greatest effect on TA. It is the dose of acid that reacts with the carbonate alkalinity portion of the total alkalinity that does the work. Maintaining a low pH with lots of little doses of acid will slowly bring your TA down but not as fast as one larger dose.

I cant think of any reason why a SWG would buffer to a pH of 7.6, I’ve never heard that before.

-Edited for auto spell check correction-

 

[cfherrman]

For extra information rain water has no ch but will pick it up from surfaces as it washes over them and then into your pool.

 

[drichitt]

I cant think of any reason why a SWG would buffer to a pH of 7.6, I’ve never heard that before.

I went back and re-read the manual and it appears what it is saying is that a SWG system will normally stabilize at a PH of approximately 7.6?

From Page 28 of the Jandy AquaPure SWG Operating Manual.....
7. The pH condition resulting from the operation of the salt water chlorination system is close to neutral. However, other factors usually cause the pH of the pool water to rise. Therefore, the pH in a pool chlorinated by a salt water system tends to stabilize at approximately 7.6. If the pool pH rises above 7.6 have a pool professional test to see if other factors such as high calcium hardness or total alkalinity are the cause and then balance accordingly.