Scale, CSI, Scaletech

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R

Russmd

Well-known member
May 14, 2013
159
Los Angeles, CA
Pool Size
40000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
We have a severe problem with water hardness in my area and my pool and salt cell frequently gets scaled over despite my best efforts. I recently drained my pool, had it blasted and washed, and refilled. I'm working at chemical balance right now - Ca is good at 300 and I'm using the lower pH/aeration technique to work at bringing the initial TA of 200 down to around 70. I'm at 150 right now. Watching CSI, now just below 0.
When the guys blasted and washed the pool, they recommended I use Scaletech and gave me a bottle to put in after refilling (haven't done so yet). They then recommended using Beautech periodically. My question is- with Ca of 300, TA 70-80 (ultimately), and the CSI in the correct range, should I still put in the Scaletech/Beautech? Wil they lower my Ca too much? Is there any benefit or detriment if the other numbers are good?
Thanks,
Russ
 
If you keep your CSI negative, then scale control products will be mostly unnecessary. They won't hurt anything by using them and the only detriment is they will add to the phosphate load in your water. However, it's takes very high levels of phosphates to cause any kind of phosphate scaling issues so there's not a lot of worry there. It depends a lot on the particular chemistry of the scale inhibitor that is used, but it will not cause your calcium levels to drop significantly. Remember that a scale inhibitor does not remove calcium from the water, it simply chelates the calcium so that the calcium ion is more stable in solution at higher pH.

I would use scale product that is designed for salt water pools because not all scale control chemicals work well when the TDS is high as in salt water pools.


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Thanks for both responses. Scaletech does say good specifically for salt pools in its documentation.
The question about the fill water is excellent - I should have thought of testing that before! Well, I just did. Out of the fill hose pH is 8.0 and TA 140.

So, yesterday, the pH was 7.6 and TA 150. I added acid to target 7.2. I aerate the pool with a waterfall spillway from the spa into the pool, jets turned up, and Kreepy Krauly on with the hose disturbing the surface. I also leave the spa bubbles on for most of the day (80% of water returns to pool through spa). Today (24 hours later) I retested. pH 7.2, TA still 150. Would you please explain to me what the time course I should expect is for the TA to start coming down? Should I wait for the pH to come up some before lowering again to 7.2 or just keep adding acid daily to keep at 7.2 until TA comes down? I don't want to harm any metal with the low pH.

Appreciate the help.
Russ
 
How cold is the water?

Acid/aeration is harder to do when the water is cold simply because colder water will outgas less CO2 and that is the primary mechanism for raising pH. You need to let the pH come up to at least 7.6 before dropping it again. It's the addition of acid that consumes TA and so the larger the delta in pH, the more likely it is you will measure a drop in TA.

Trick is though, you can't be adding high TA fill water. You don't have any leaks or excessive fill water additions, do you?


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It is cold, water about 65F now. No leaks, very little fill going in now. I did just install a water softener in the automatic fill line (type that absorbs calcium, not salt exchange). I understand to watch that calcium doesn't get low. I'm going to test that water tomorrow.
Thanks
 
OK, so I'm getting a little frustrated - should I be? I just tested my water again.
FCL - 3.5
pH - 7.8
TA - 175
CYA - 70
CA - 300
Salt - 2800

Last week I brought the pH down to 7.2. Aerated with spillway from spa on all day, kreepy krauly, spa bubbles each day for hours. Just got he numbers above. pH back up to 7.8 but not even a dent in the TA from previous! No external fill water added other than one day of rain. Why can I not get the TA down?

Thanks,
Russ
 
Russ,

It is not a one time deal. Here is how I do it... Measure and record pH and TA. Add acid to reduce pH to 7.0. Turn on aeration. In three or four hours test pH and TA again, when pH gets back to about 7.3 or 7.4, add more acid to reduce it to 7.0. You just keep doing this, over and over. Each time you do TA will get a little lower. Once your TA gets a little less than what you want, say 50 or 60, you stop adding acid and keep aerating until the pH gets back up to 7.6 or so.

With a TA of 175, I'd set aside a weekend to do it..

Thanks for posting,

Jim R.
 
In a 30,000 gallon pool using the information provided it will take 124 fluid ounces of full strength muriatic acid to reduce the pH from 7.8 to 7.2. Doing so will consume ~ 16ppm TA. If you use the 10mL water sample test for TA (25ppm/drop) you almost definitely will not see a change. If you use the 25mL water sample TA test (10ppm/drop) you will just barely be able to see that kind of change assuming you get the drop count correct.

As Jim pointed out, this is a process. You need to do several acid/aeration cycles in a row to see the effect. My suggestion would be that you lower pH to 7.0 and aerate up to 7.6, then repeat the acid addition again. The rate of CO2 outgassing is faster from 7.0 to 7.5 than it is from 7.6 to 8.0 (i.e., it's not linear). SO waiting to get to 7.8 just adds extra time for no useful purpose.

Rain water will have a small amount of alkalinity to it (it will absorb CO2 from the atmosphere) and, when it contacts stone material, it will leach carbonates from the stone. So it is possible for rainwater to add to the carbonate alkalinity.
 
Thanks for the excellent info. Before having read this latest information, I did the weekend routine but got to about 7.2 before allowing it to get to 7.6. Did this three times over the weekend. As predicted, barely see a drop, maybe 20 points, but I was using the 10 ml sample. I will try the 7.0 to 7.6 routine and the 25 ml sample - I was concerned about 7.0 and everything I hear about low pH destroying metal, especially the heater. I have no way to bypass it.
Russ
 

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7.0 is fine. A heater core would have to be exposed to water with a pH lower than 6 for there to be any real start to corrosion and, even in that case, it would have to persist for months. When we talk about heater corrosion, we're talking about people who let their TA fall to 0 which means the pH is down somewhere in the 4.5 range. Or people that leave trichlor pucks in their skimmer baskets causing low pH/TA water to develop and be sucked straight into the pump/filter/heater.

You're fine at 7.0.


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Just some follow up. I think I'm getting a handle on it now thanks to your help. Several days ago, I added acid to get it to 7.2 and aerated. I just checked and pH is only up to 7.3 but TA is down to 90. So now, pH rise is much slower, I guess as expected as TA has fallen. I think this should just about do it for now. I'll let it settle out for a week and hope we'll be about 7.6 and 80. That would put my CSI at around -0.36, just where I want. Thanks again to all.
Russ
 
Ok, would you please enlighten me a little? I let things settle in pretty well. CYA is 70, TA 85. I had pH at 7.5 last week. Now, all of a sudden, pH is almost 8 but TA hasn't changed? I thought with TA in range, the pH should be more stable and have less of a big swing? No water added, no other changes.
 
My pH is never "stable"; it rises all the time. Ive gotten it to slow down over the years but only by maintaining a TA of 60ppm and adding 50ppm borates to the water. Even with all that, I still have to add 1-1/2 pints of acid every 10days or so.


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Both the SWG and the Kreepy (disrupts the water surface) will have an upward effect on your pH. I notice a pretty significant difference in pH rise when I have the Kreepy plugged in versus when I do not.

While you can reduce the pH rise overall with a lower TA (mine is at around 60-70), you'll always need muriatic acid on hand to bring the pH back down from time to time. This is totally normal.
 
Thank you. So I'll try to get the TA down a little more, to 60 or so. Not sure I want to start messing with Borates yet, need to do some more reading about that!
Russ
 
At around 7.8 my pH remains stable for some time before rising. Trying to keep the pH any lower, it rises quickly. The real secret is finding that right TA and pH where you have some stability, and a CSI in the correct range.
In my case (with borates) that's TA about 60-65, pH about 7.8 and CSI between -0.15 and -0.3.
YRMV.
 

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