How to reduce Alkalinity without dramatically decreasing pH.

[DavidArmenB]

I just had my Pool&Spa resurfaced with StoneScapes Mini Pebble. The start up procedure calls for reducing Alkalinity to 80ppm and reducing pH to between 7.2 and 7.6 on day One after Pool is filled.

The issue is my potable fill water has a pH which is in the range, but the Alkalinity is 180ppm.

Fill Water Results:
pH: 7.5 - 7.6
Total Alkalinity: 180ppm
Calcium Hardness: 180ppm
Salt: 410ppm (digital meter)

After the fill, I added 2 gallons of 14.5% Muriatic acid which decreased the pH to below 7.0 and decreased Alkalinity to 130ppm

My question is, when starting up new plaster, is it okay to reduce Alkalinity in the usual slow way, whereby you add enough acid to decrease alkalinity while only decreasing pH to 7.2, then aerate to bring back pH while retaining the Alkalinity levels, and repeat this process until Alkalinity is in range?
The instructions make it seems like you are supposed to do this in one day, on day 1 of start up. Won’t adding that much acid in one go to decrease Alkalinity from 180ppm to 80ppm decrease pH to severe levels?

 

[Poolnerdgrandma]

Following. My TA is very high, and even adding MA pretty often, it's not coming down much. We had a very dry spring, and I had to add a lot of fill water to keep up with evaporation.

 

[PoolStored]

My question is, when starting up new plaster, is it okay to reduce Alkalinity in the usual slow way, whereby you add enough acid to decrease alkalinity while only decreasing pH to 7.2, then aerate to bring back pH while retaining the Alkalinity levels, and repeat this process until Alkalinity is in range?

Best way to do it safely.

The instructions make it seems like you are supposed to do this in one day, on day 1 of start up. Won’t adding that much acid in one go to decrease Alkalinity from 180ppm to 80ppm decrease pH to severe levels?

Yes, don't lower pH below 7.2.

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

 

[DavidArmenB]

Best way to do it safely.

Yes, don't lower pH below 7.0.

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

Thank you! I will do it slowly the way I normally do it. There’s no issue with turning on pump with these Alkalinity levels? I have already bypassed heater and removed swg for dummy pipe for first 28 days because of the plaster dust.

 

[PoolStored]

You should follow the StoneScapes Mini Pebble startup guide. Do you have it?

 

[PoolStored]

Start-up guides don't explain why they recommend the water chemistry they do. Most start-up water chemistry is biased towards a positive CSI. 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.

 

[DavidArmenB]

Following. My TA is very high, and even adding MA pretty often, it's not coming down much. We had a very dry spring, and I had to add a lot of fill water to keep up with evaporation.

That’s very interesting! How high? I’ve never had an issue lowering Alkalinity with Muriatic acid. I usually put around 50oz 31.45% Muriatic acid to reduce pH to ~7.2 which also reduces alkalinity by about 20ppm for my 16,000gal pool. I then wait a few days for pH to rise by natural aeration and aeration that my SWG causes by the small hydrogen bubbles. It can take a few weeks but I do this as many times as needed to reduce Alkalinity to ideal levels.

Is your issue that Alkalinity isn’t dropping with Acid or it is somehow ricing back up?

 

[JamesW]

Try to maintain the CSI at about 0.0 and you should be fine.

Don't lower the pH below 7.2.

 

[DavidArmenB]

Start-up guides don't explain why they recommend the water chemistry they do. Most start-up water chemistry is biased towards a positive CSI. 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.

That’s very interesting! Hard start-ups go against this idea, as they cause CSI/LSI to be very negative, which I find very curious. I did not do a hard start up but my water is currently in the very negative range. How can I make my CSI so positive? Keep Alkalinity high and increase pH to 8.0??

 

[onBalance]

Reading the below post will explain why it would be best for your plaster job to have the pool water at a slightly positive CSI for a couple of weeks. Hard or Hot startups are not good for new plaster.
I suggest that you go easy on lowering the alkalinity too quickly and the pH too low.

The Best Plaster Pool Startup

Additional clarifications on the Bicarb (or Positive CSI) Startup. THE BEST PLASTER POOL START UP How a startup program deals with and prevents the detrimental process of “plaster dust” forming in newly plaster pools is the key in helping to preserve a quality plaster finish that will last 20+...

www.troublefreepool.com

 

[JamesW]

The fortunate and good news is that filling pools with water that has an CSI of +0.5 or above prevents calcium hydroxide from being dissolved from the plaster in the first place.

CSI only applies to calcium carbonate.

Calcium hydroxide has an entirely different formula for determining saturation.

Calcium hydroxide is about 122 times more soluble in water than calcium carbonate.

So, the calcium hydroxide is going to dissolve from the plaster unless you reach saturation of calcium hydroxide, which is based on the concentrations of calcium and hydroxide.

You won’t be able to reach saturation of calcium hydroxide.

You would probably need a pH of about 12.4 to prevent the calcium hydroxide from dissolving.

In my opinion, maintaining a 0.0 CSI reduces the risk of scaling because a CSI over 0.0 can begin to deposit scale.

However, as you have the most experience with plaster, I would trust your recommendations over my estimation of what is a better procedure.

 

[JamesW]

If the CSI is 0.0, then there should be enough carbonate to react with the plaster to convert calcium hydroxide to calcium carbonate.

If the process is a substitution, then having extra carbonate might be beneficial.

Ca(OH)₂ + CO₃^2- --> CaCO₃ + 2OH ^-

 

[JamesW]

This is similar to how fluoride helps strengthen teeth.

Fluoride ions (F^-) replace hydroxyl groups (OH^-) in hydroxyapatite to form fluorapatite in the tooth enamel.

Ca₁₀(PO₄)₆(OH)₂ + 2F^- --> Ca₁₀(PO₄)₆F₂ + 2OH^-

Fluorapatite is less soluble than hydroxyapatite.

 

[onBalance]

To not hijack this thread, I have addressed some of the comments above in my post about the Bicarb startup.
See this post:

The Best Plaster Pool Startup

Additional clarifications on the Bicarb (or Positive CSI) Startup. THE BEST PLASTER POOL START UP How a startup program deals with and prevents the detrimental process of “plaster dust” forming in newly plaster pools is the key in helping to preserve a quality plaster finish that will last 20+...

www.troublefreepool.com

 

[DavidArmenB]

A lot of incredible information in these posts!! I’m very appreciative!