- Jul 21, 2013
- 64,776
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Good. Follow that.
Use small doses of chemicals and test between doses until you learn how your pool responds.
CO2 pH Control
- Thread starter crosby1612
- Start date
Good. Follow that.
Use small doses of chemicals and test between doses until you learn how your pool responds.
Recommendation from the National Plaster Council on new plaster pools is a TA of 80 - 100. Where are you getting TA of 60 from?Get this meter and begin to manage the CSI.
PC60 Premium Multiparameter (pH/EC/TDS/Salinity/Temperature) Pocket Tester/Meter Kit-Apera Instruments
The Apera Instruments PC60 Multi-parameter Tester/Meter simply tests pH/EC/TDS/Salinity/Temperature for regular aqueous solutions such as hydroponics, aquaculture, pools& spas, tap/drinking water, water treatment, cooling towers, etc.aperainst.com
Begin to lower the TA, keep the pH at about 8.0 to 8.3 and adjust the CH to balance the CSI.
Note that as the water warms up, the CSI will increase, so anticipate this when adding calcium and do not add too much.
Get the TA down to about 60 ppm.
60 ppm TA will minimize the carbon dioxide loss and the subsequent pH rise that happens due to CO2 loss.
The most important thing is to keep the CSI between -0.3 and 0.0.
Where does the National Plaster Council get 80 to 100?
If you keep the TA at 80 to 100, plan to go through that process again.
High TA is the main reason people fight continuously rising pH.
Low CSI can cause the plaster to dissolve and raise the TA and pH.
Low pH also causes there to be too much carbon dioxide and it makes the pH rise.
Most people think that keeping the pH low and TA high is the way to fight rising pH but that is exactly the wrong thing to do.
- Jul 21, 2013
- 64,776
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
The normal CSI guidelines are not applicable to new plaster finishes under 30 days old. It is actually necessary, to achieve a smooth and dense surface, to have about a +0.5 CSI during the first 30 days. This is because the plaster (cement paste) surface contains about 20% calcium hydroxide, which is somewhat soluble in balanced and slightly positive CSI water and can be dissolved away. The plaster surface needs to be "carbonated" before the CSI should be lowered to the acceptable and balanced range. And that generally is achieved during the first month under balanced water.
The CSI is Reliable for Plaster-based Pools
Using the Calcium Saturation Index (also known as the LSI in the pool industry) as a guide for maintaining proper pool water balance and to protect pool plaster, including quartz and pebble finishes, has become a mainstay in our industry for good reason. Several experiments have been conducted...
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People need to be very careful and brush a lot to avoid scaling.
If you go with a +0.5 CSI, you need to really watch the levels and keep them in tight control.
If scaling begins, you need to get the CSI down fast to avoid it getting out of control.
- Jul 21, 2013
- 64,776
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
They know more than I do, so I will defer to them.
My main concern is scaling that can get started and get out of control.
I would go with a balanced 0.0, but a higher CSI might work better to make the plaster stronger as long as you can avoid scaling.
- Jul 21, 2013
- 64,776
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
People rarely can get a new plaster startup to +0.5. Some positive CSI between 0 and +0.5 is good and a reason not to obsess with TA value.
Their testing is known to be bad, almost comically bad. I can able to get my CYA and copper levels lowered by just taking the same water sample to another store.
Don’t make any adjustments based on a pool store test or you’ll likely regret it later.
Calcium carbonate solubility in water = 0.013 g/L (25 °C).
Solubility product (Ksp) = 3.3×10−9.
_______________________________________________________________
Calcium hydroxide solubility in water = 1.73 g/L (20 °C).
Solubility product (Ksp) = 5.02×10−6
_______________________________________________________________
Calcium Hydroxide is about 133 times more soluble than calcium carbonate.
The Ksp of calcium hydroxide is about 1,521 times higher than the Ksp for calcium carbonate.
(5.02 x 10^-6)/(3.3 x 10^-9) = 1521
So, just raising the CSI a little bit is not going to afford a lot of protection for calcium hydroxide.
To get a saturated solution of calcium hydroxide with 300 ppm of calcium Hardness, you would need a pH of about 12.61.
Solubility product (Ksp) = 3.3×10−9.
_______________________________________________________________
Calcium hydroxide solubility in water = 1.73 g/L (20 °C).
Solubility product (Ksp) = 5.02×10−6
_______________________________________________________________
Calcium Hydroxide is about 133 times more soluble than calcium carbonate.
The Ksp of calcium hydroxide is about 1,521 times higher than the Ksp for calcium carbonate.
(5.02 x 10^-6)/(3.3 x 10^-9) = 1521
So, just raising the CSI a little bit is not going to afford a lot of protection for calcium hydroxide.
To get a saturated solution of calcium hydroxide with 300 ppm of calcium Hardness, you would need a pH of about 12.61.
Ca(OH)2 + CO32- --> CaCO3 + 2OH-
Having extra carbonate can help substitute carbonate for hydroxide, so it might be more beneficial to have a higher CSI even if the solution is not saturated for calcium hydroxide.
The main risk is if the plaster dust is not managed and scaling begins, the scaling can quickly get out of control.
All of that released hydroxide can make the pH go very high very fast.
In any case, careful management of the plaster in the first thirty days is critical to having good plaster that looks good and lasts a long time.
Crosby,
Newly plastered pools (less than 30 days) have completely different needs than when the plaster has been under water for at least one month. Keep that in mind as I offer suggestions for you to follow for the first month of your new pool.
Since your plaster is less than 30 days old, the pH will always be very difficult to keep under 8.3. That is just the way it is. Fortunately, there is one way to ease that difficulty, and that is by maintaining the CSI (or LSI) at about +0.4 to +0.5 for 20 to 30 days. To achieve that high CSI, it is best to have a high alkalinity if possible, and the pH between 7.8 and 8.3. The calcium hardness should never be adjusted upward (if needed) until the pH is under 8.0. Daily additions of small amounts of acid will probably be needed for the first two to three weeks.
The following is an explanation about the above program, and it only applies to new plaster, not a plaster pool that is beyond 30 days. If or when the pH is low and/or the alkalinity is low, and the CSI is below +0.4, some plaster material (calcium hydroxide) will dissolve into the pool water and immediately cause the pH to rise dramatically. That is exactly why the pH in your pool water was tested at 8.7 (if I read that above correctly). Only by maintaining the CSI at a high level will prevent the dissolution of calcium hydroxide from the plaster surface. Once 30 days have past, there is no longer any calcium hydroxide on the plaster surface because it has been carbonated. It is no longer a problem to deal with. I have proven the above information through many experiments.
One other point, do not use liquid chlorine for the first month unless you add acid at the same time. Liquid chlorine has a very high pH and could cause scaling when added if not neutralized by adding acid at the same time and brushing afterwards to remove scale (if present) and to circulate the water.
My suggestion to you right now is to add acid and bicarb at the same time to lower the pH. If you add 7 lbs. of bicarb for every gallon of 31.45% acid, that will negate any change to the TA. But it will lower the pH. I would proceed to get the CSI to a higher level mentioned above. Brushing is always necessary and vital for new plaster pools. Thousands of pools are successfully using the Bicarb Startup program or the Orenda's Positive LSI Calcium startup program.
Once your pool is beyond 30 days, maintaining the CSI near the 0.0 level, and maintaining a low TA will help ease the constant pH rise and have to add acid constantly. Of course, the concept of using carbon dioxide is a good choice for pH control, but only when the alkalinity has been lowered.
If anyone sees something that I missed or has questions, please respond. Thanks.
Newly plastered pools (less than 30 days) have completely different needs than when the plaster has been under water for at least one month. Keep that in mind as I offer suggestions for you to follow for the first month of your new pool.
Since your plaster is less than 30 days old, the pH will always be very difficult to keep under 8.3. That is just the way it is. Fortunately, there is one way to ease that difficulty, and that is by maintaining the CSI (or LSI) at about +0.4 to +0.5 for 20 to 30 days. To achieve that high CSI, it is best to have a high alkalinity if possible, and the pH between 7.8 and 8.3. The calcium hardness should never be adjusted upward (if needed) until the pH is under 8.0. Daily additions of small amounts of acid will probably be needed for the first two to three weeks.
The following is an explanation about the above program, and it only applies to new plaster, not a plaster pool that is beyond 30 days. If or when the pH is low and/or the alkalinity is low, and the CSI is below +0.4, some plaster material (calcium hydroxide) will dissolve into the pool water and immediately cause the pH to rise dramatically. That is exactly why the pH in your pool water was tested at 8.7 (if I read that above correctly). Only by maintaining the CSI at a high level will prevent the dissolution of calcium hydroxide from the plaster surface. Once 30 days have past, there is no longer any calcium hydroxide on the plaster surface because it has been carbonated. It is no longer a problem to deal with. I have proven the above information through many experiments.
One other point, do not use liquid chlorine for the first month unless you add acid at the same time. Liquid chlorine has a very high pH and could cause scaling when added if not neutralized by adding acid at the same time and brushing afterwards to remove scale (if present) and to circulate the water.
My suggestion to you right now is to add acid and bicarb at the same time to lower the pH. If you add 7 lbs. of bicarb for every gallon of 31.45% acid, that will negate any change to the TA. But it will lower the pH. I would proceed to get the CSI to a higher level mentioned above. Brushing is always necessary and vital for new plaster pools. Thousands of pools are successfully using the Bicarb Startup program or the Orenda's Positive LSI Calcium startup program.
Once your pool is beyond 30 days, maintaining the CSI near the 0.0 level, and maintaining a low TA will help ease the constant pH rise and have to add acid constantly. Of course, the concept of using carbon dioxide is a good choice for pH control, but only when the alkalinity has been lowered.
If anyone sees something that I missed or has questions, please respond. Thanks.
Just to clarify for the OP, never mix chemicals together.
Always add separately giving time for one chemical to mix into the pool water before adding a different chemical.
Ideally, pour into the return stream and also brush the pool to help mix added chemicals.
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- Oct 25, 2015
- 5,801
- Pool Size
- 28000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60 Plus
I put in a home made CO2 system for my pool a few weeks ago. Seems to be working well and I controlled it with a solenoid valve set up I cobbled together with a combination of pool parts and brewing parts. One of the main reasons I did mine was I use a lot of acid and hated the jug-lugging. It's also helpful to me since I am in the final leg of a 3 week trip out of the country and didn't have a way to add all that acid (I use about a gallon every 3 days). Where did you find the cheap source of CO2? Mine is $44 for 20 lb. and seems to be the going rate around here. I still need to lug a 20 lb cylinder to the pool pad about every month but that seems easier that the jug lugging and I think it's a little cheaper than acid price that seems to have gone up almost double since Covid. Here's a link to my thread if you want to check it out.
It helped that I raised my pH to 7.9-8.0 and I have TA still pretty low (~70 ppm). A challenge for me is that I'm on well water with TA 230 in the make up. Now that I'm no longer adding acid my TA is creeping up. So I'll either have to go back to acid addition or I'll have to put in an RO unit for the make up water.
I hope this is helpful.
Chris
- Oct 25, 2015
- 5,801
- Pool Size
- 28000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60 Plus
Adding a update on this system. Bottom line is I love it. It did superb during my 3 week absence for our Italy trip. Only change I had to make was to modify the program slightly so it would persist through a power outage. The ESP 32 has plenty of memory to use for this so I made sure the most recent settings are saved and read on boot up. Easy peasy using my ChatGPT to modify the code. I'm now about two months in and have a few things worth mentioning in case anybody else want to give it a try:
I hope this is helpful.
Chris
- @JamesW calculations are turning out to be very accurate -no surprise!
- The solubility calcs indicated I needed to reduce CO2 by a factor of 10. I reduced by a factor of 5 before we left and found the spa pH was very low - about 7 or a tiny bit lower. It got so low that I precipitated white flakes in the spa that are probably salt or calcium. Very fine flakes that look like it snowed them in the spa. The circulation from my filter pump flows back the the spa jets and over flows to the pool. Once diluted in the pool the pH was maintained at about 7.8 which was lower than my target of 8.0
- Also, I could see sort of a squirt of a couple hundred tiny bubbles with each pulse.
- So I reduced the pulse time to .1 seconds and adjusted the number of pulses and the bubbles got fewer and fewer then just disappeared. At this point I believe the CO2 injected is completely dissolved. I had to extend the number of pulses to deliver sufficient CO2 and this was some fine tuning that resulted in about 1/10th the amount of CO2 based on my previous calculations. Exactly what was predicted by our resident Chem E expert.
- Now I just monitor the pH and have moved the probe so it's before the injection point. It seems to be pretty accurate and when it trends over pH 8 I just give it a manual extra series of pulses. pH comes right back down. Right now I use 200 pulses per series with 12 second interval between pulses and seems to be just right.
- As expected my TA is trending up because my pool make up water is from a well that's about 230 ppm TA. Solution for that is in the works which will use an under counter RO unit mounted in a large plastic box out at the pad. This will become my new make up water for the pool. Pool uses about 50 gal per day so sizing works well. Most of these units can make up to 80 gal per day. I think the level control squirts in about 1-2 gal at a time so the 3 gal tank should work about right.
I hope this is helpful.
Chris
Low pH is not expected to precipitate calcium or any other ionic compound.
You can also add muriatic acid periodically to help manage the TA and let the CO2 manage the pH.