Rapid clouding when adding pH increaser

[TreeFiter]

Today I was sent to a pool that had turned cloudy when one of our techs added pH increaser (Sodium Carbonate). The pool is an 18x36 rectangle (about 24,000 gal.), vinyl liner, with a SWG.

My initial assumption was that the Calcium Hardness was probably too high, and when the pH came up, the water precipitated CaCO3. I tested the water with a TF-100, and I'm kind of surprised with what I found, and confused as to why it turned cloudy. This pool has had some issues this season. It was struggling to maintain chlorine levels, and cloudy every other week for the first half of the season. I hit the pool hard with chlorine, and stayed on it for about 4 days. (Not quite a SLAM by definition, but the best I can do given the circumstances) From that point on the pool has been stable, and has had no problem maintaining adequate FC levels. The tech that regularly takes care of this pool has had problems every time he adds pH increaser with clouding. I've experienced similar rapid clouding in other pools, but typically it dissipates within a day or so.

This time the pool clouded completely, and there was a renter at the house, so they called and complained, and I was sent out to see what I could do. Here is what I found:

CH=150
TA=80
pH=8.0
FC=4
CYA=30

I talked to the tech about the chemistry he observed the day before, and the only differences would have been in pH and TA. He said the pH was down around 7.0 so he added 4lb of pH increaser.

When I punch these numbers into the PoolCalculator, I see that the CSI goes from negative to positive with this change in pH, but it doesn't seem to push it far enough to justify the instant clouding of the entire pool.

Any thoughts?

 

[JamesW]

Clouding is common with sodium carbonate, especially if added in conjunction with any calcium based product such as calcium hypochlorite or calcium chloride. I never use sodium carbonate. I only use sodium bicarbonate because if the ph is going too low, the ta is too low and raising it will keep the ph in check.

With a swg and a ta of 80, there's no reason for the ph to be low. Maybe he's not reading the ph correctly. A swg is mostly ph neutral. I never have to raise or lower the ph on a swg pool once the ta is correct.

If he's adding ph increaser or decreaser on a regular basis, he's doing something wrong.

 

[TreeFiter]

With a swg and a ta of 80, there's no reason for the ph to be low. Maybe he's not reading the ph correctly. A swg is mostly ph neutral. I never have to raise or lower the ph on a swg pool once the ta is correct.

If he's adding ph increaser or decreaser on a regular basis, he's doing something wrong.

I agree. We typically see pH drifting upwards, but thats because most of our guys keep the TA too high. Based on the pH being around 8.0 after adding the increaser, I'm inclined to think the pool probably didn't really need it. Four pounds of Sodium Carbonate in a pool that size should raise the pH by about 0.6. That means it had to be somewhere around 7.4 when he added it. But even so, I wouldn't expect such intense clouding when the CSI is only about 0.16.

I have seen the clouding you mentioned with Cal-Hypo, and in pools with high CH or high pH, Cal-Hypo by itself will cloud the pool. The clouding that has been happening in this pool is rapid and vigorous. It expands outwards rapidly. I've seen it in other pools too, but I haven't been able to find a reason for it.

 

[JamesW]

I would suspect that the pH was actually good. I don't know why, but sometimes an initial pH test reads wrong and subsequent tests read correctly. Perhaps the reagent is separating and the initial test mixes the reagent when the bottle is turned upside down.

A tech should know when a reading doesn't make sense and double check the result by retesting.

For a SWG pool with a TA of 80, the only reason the pH would be low is if something acidic were being added.

The only thing acidic a person should need to a SWG pool is cyanuric acid. Even then, the effect is minor and temporary.

In any case, I would stop using sodium carbonate completely and you won't have any more problems.

 

[jv92red]

I'm going to take a guess and say someone made a mistake and when trying to supplement the SWC after a summer swim party with some liquid chlorine but instead of grabbing the Chlorine bottle they grabbed the MA bottle. How else would the pool drop to a 7.0? I keep both of these on hand from Home Depot and the 128oz jugs look EXACTLY the same from each other. They only come out of different colors boxes and have different labeling of course. But I always take a second look at the label when adding cause you don't want to make that mistake...

Like James said, something doesn't make sense. Either a test was read wrong or someone dumped in some MA by accident. In my pool I ONLY drift up with PH. No matter what the TA is, and I also added borates to help mitigate the PH drift but between the SWG and the 2' drop for my spa spill over there is always plenty of aeration to drive up my PH.

 

[TreeFiter]

I don't think the pH being low is that big of a mystery. Rain is acidic. Its not uncommon to get enough rain to lower pH. Regardless of how the pH may have gotten low, or if the tech made a mistake, the numbers still don't explain the clouding. The CSI just isn't high enough.

 

[JoyfulNoise]

You have to realize that when adding any form of dry chemical, even prediluted, you're going to get "hot spots". If your tech dumped the powder in, then the water volume around the powder probably shot ip way past 8.0 pH and I'd bet the localized CSI went well above scaling. Even with 150ppm CH, you can still scale out calcium carbonate if the local pH and carbonate hardness is high enough.

Reducing the pH and filtration should clear the cloudiness with time.


Sent from my iPhone using Tapatalk

 

[chem geek]

First off, something is wrong with the numbers or quantities. Adding 4 pounds of soda ash to 24,000 gallons wouldn't go from 7.0 to 8.0 in pH. I think it was actually closer to 7.1 in pH and the starting TA was around 60 ppm in which case one ends up with 7.89 pH and 79 ppm TA which are close to what you saw.

Local clouding can occur with a negative CSI in the pool water because until the product is completely diluted a pH Up of sodium carbonate is high in both TA and pH. The following shows what happens when diluted in pool water with the numbers given. In addition to the Calcite Saturation Index (CSI), I also show the Calcium Carbonate Precipitation Potential (CCPP) which shows the maximum amount of calcium carbonate in ppm (mg/L) that can precipitate (it starts off mostly limited by the 150 ppm of CH).

Dilution of 4 pounds soda ash in:

Gallons .... pH ........ TA ...... CSI ..... CCPP
..... 10 .... 11.45 .. 45,324 .. +2.27 .. 149.2
... 100 .... 11.05 .... 4,586 .. +2.25 .. 149.1
. 1000 .... 10.36 ....... 513 .. +2.10 .. 148.8
. 2500 ...... 9.91 ....... 241 .. +1.87 .. 141.7
. 5000 ...... 9.51 ....... 151 .. +1.58 .... 69.0
. 7500 ...... 9.25 ....... 120 .. +1.34 .... 40.1
10,000 ..... 9.02 ....... 105 .. +1.14 .... 25.6
15,000 ..... 8.61 ......... 90 .. +0.73 .... 11.0 <--- limit where we normally see scaling
20,000 ..... 8.17 ......... 83 .. +0.29 ...... 3.7 <--- limit where we sometimes see water be duller to over-saturation
24,000 ..... 7.89 ......... 79 .. +0.01 ...... 0.1

There is no mystery here. During dilution of soda ash the CSI is very high and there will be cloudiness. This almost always happens unless there is almost no CH at all in the water. It is only when the product is more fully diluted that the cloudiness will normally dissipate, but as shown above for this pool the cloudiness would persist at least until it got to being in 2/3rds of the water. After that, the calcium carbonate should very slowly dissolve into the water since it will still be slightly over-saturated, but depending on how big the calcium carbonate clumps were, this could take some time.

One has to add soda ash VERY slowly to a pool and even then should not use the full dose to get to a CSI of 0 right away. For this pool, lowering the pH to 7.5 using acid should help and then if one wants further adjustments to increase TA or CH one can do so slowly and carefully.

 

[TreeFiter]

First off, something is wrong with the numbers or quantities. Adding 4 pounds of soda ash to 24,000 gallons wouldn't go from 7.0 to 8.0 in pH. I think it was actually closer to 7.1 in pH and the starting TA was around 60 ppm in which case one ends up with 7.89 pH and 79 ppm TA which are close to what you saw.

Local clouding can occur with a negative CSI in the pool water because until the product is completely diluted a pH Up of sodium carbonate is high in both TA and pH. The following shows what happens when diluted in pool water with the numbers given.

Dilution of 4 pounds soda ash in:

Gallons .... pH ........ TA ...... CSI
..... 10 .... 11.45 .. 45,324 .. +2.27
... 100 .... 11.05 .... 4,586 .. +2.25
. 1000 .... 10.36 ....... 513 .. +2.10
. 2500 ...... 9.91 ....... 241 .. +1.87
. 5000 ...... 9.51 ....... 151 .. +1.58
. 7500 ...... 9.25 ....... 120 .. +1.34
10,000 ..... 9.02 ....... 105 .. +1.14
15,000 ..... 8.61 ......... 90 .. +0.73 <--- limit where we normally see scaling
20,000 ..... 8.17 ......... 83 .. +0.29 <--- limit where we sometimes see water be duller to over-saturation
24,000 ..... 7.89 ......... 79 .. +0.01

There is no mystery here. During dilution of soda ash the CSI is very high and there will be cloudiness. This almost always happens unless there is almost no CH at all in the water. It is only when the product is more fully diluted that the cloudiness will normally dissipate, but as shown above for this pool the cloudiness would persist at least until it got to being in 2/3rds of the water. After that, the calcium carbonate should very slowly dissolve into the water since it will still be slightly over-saturated.

You are probably right about the numbers being off. The numbers I was given were taken from test strips. The numbers I measured after were TF-100.

I understand that some clouding is common, but we are talking about the entire pool clouding over to the point where I could only see the liner about a foot down the wall. It just seems like what I'm seeing is not something that would be expected from a pool with what would be considered a low Calcium Hardness while dealing with pH in a fairly normal range, and TA that would be considered low by industry standards. If these conditions are conducive to rapid precipitation of calcium carbonate, just about every pool out there would cloud over when pH increaser is added. It doesn't seem to happen in the majority of the pools I deal with, but there are a select few that seem to behave differently.

 

[chem geek]

Well when I first started out using Trichlor and used pH Up (soda ash) I ALWAYS noticed cloudiness and it always took a while to dissipate and it seemed that how long it took was largely a function of the CSI and pH. In the pool example you gave above, the pH is high at 8.0. Could it be that in your other pools when adding pH Up you didn't overshoot and instead got closer to 7.5 or that in other pools you didn't go to a CSI near 0 but was slightly negative?

Or perhaps the starting CH in this pool was indeed much higher and that what you are measuring is the CH leftover after a bunch of calcium carbonate precipitated and this precipitate is what is remaining as cloudiness. If that is the case, then lowering the pH may result in the CH rising as the calcium carbonate gets dissolved. If you cannot see the pool bottom, there may even be solid calcium carbonate precipitate at the bottom or there may be scaling on pool surfaces.

 

[TreeFiter]

Well when I first started out using Trichlor and used pH Up (soda ash) I ALWAYS noticed cloudiness and it always took a while to dissipate and it seemed that how long it took was largely a function of the CSI and pH. In the pool example you gave above, the pH is high at 8.0. Could it be that in your other pools when adding pH Up you didn't overshoot and instead got closer to 7.5 or that in other pools you didn't go to a CSI near 0 but was slightly negative?

Or perhaps the starting CH in this pool was indeed much higher and that what you are measuring is the CH leftover after a bunch of calcium carbonate precipitated and this precipitate is what is remaining as cloudiness. If that is the case, then lowering the pH may result in the CH rising as the calcium carbonate gets dissolved. If you cannot see the pool bottom, there may even be solid calcium carbonate precipitate at the bottom or there may be scaling on pool surfaces.

I think you might have hit the nail on the head with regard to the CH measurement being a measure of how much was left after the reaction. That would make perfect sense.