Ideal pH/TA for 68,000 gallon pool?

[BakingSoda]

Hello, first time posting.

We have a 68,000 gallon pool with the following equipment: BECSys3 chemical controller. Acid-Rite pH balancing system. Accu-Tab chlorination system. Avg temp 82F. Testing with ColorQ2x Pro7.

The chemical controller is currently set to bring the pH down to 7.5 (we’ve had it at 7.6 before) and keep the ORP at 815(FCL is usually around 1.6)

We are trying to find a balance to keep our alkalinity up, but also keep the pH at ideal levels as well. We are treating with Baking Soda to bring it up to 80 TA. We’ve been averaging 8-10lbs of baking soda added daily. This raises our pH up to around 7.8(on the BECSys3 sensor) after treating and our Acid-Rite system will run until it brings it back down to 7.5. Our Acid-Rite system is also eating a lot of the acid tablets and lately we go through a couple 45lb buckets a week.

I’ve read somewhere that some people let the pH go a bit higher like 7.7-7.8, but I’m not sure what the general consensus on that is. Is TA in the 60-80 range acceptable/reasonable?

Any input is greatly appreciated!

 

[kimkats]

Hi and welcome to TFP. Is this pool a public or private pool? This knowledge will change what you can and cannot do with the pool.

 

[BakingSoda]

Hi and welcome to TFP. Is this pool a public or private pool? This knowledge will change what you can and cannot do with the pool.

Thanks for the reply!

It is public.

 

[JamesW]

Acid-Rite pH balancing system.

That is sodium bisulfate, which adds a lot of sulfates.

You would be better off with muriatic acid or a CO2 system if you are a commercial pool that has to maintain certain levels of TA and pH.

Do you have code required chemistry?

If yes, what are the levels?

The chemical controller is currently set to bring the pH down to 7.5 (we’ve had it at 7.6 before) and keep the ORP at 815(FCL is usually around 1.6)

Why 815 for the ORP?

That seems high?

Do you use CYA (Cyanuric acid)?

We are trying to find a balance to keep our alkalinity up, but also keep the pH at ideal levels as well.

You can keep the TA down to as low as 50 and the pH up to 8.0 if the levels are not prescribed by code.

Our Acid-Rite system is also eating a lot of the acid tablets and lately we go through a couple 45lb buckets a week.

90 pounds of sodium bisulfate per week?

We’ve been averaging 8-10lbs of baking soda added daily.

63 pounds of baking soda per week.



As you can see, the baking soda and the acid are basically neutralizing each other and you are wasting both.

By raising the pH as high as you legally can or up to 7.9 to 8.0 and lowering the TA as much as legally possible down to 50 or 60, you can virtually eliminate both chemicals.

 

[JamesW]

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[BakingSoda]

That is sodium bisulfate, which adds a lot of sulfates.

You would be better off with muriatic acid or a CO2 system if you are a commercial pool that has to maintain certain levels of TA and pH.

Do you have code required chemistry?

If yes, what are the levels?

Why 815 for the ORP?

That seems high?

Do you use CYA (Cyanuric acid)?

You can keep the TA down to as low as 50 and the pH up to 8.0 if the levels are not prescribed by code.

90 pounds of sodium bisulfate per week?

View attachment 541764

63 pounds of baking soda per week.

View attachment 541765

As you can see, the baking soda and the acid are basically neutralizing each other and you are wasting both.

By raising the pH as high as you legally can or up to 7.9 to 8.0 and lowering the TA as much as legally possible down to 50 or 60, you can virtually eliminate both chemicals.

We’ve been discussing possibly moving to muriatic acid because we are getting calcium sulfate scaling.

The Accu-Tabs are calcium hypochlorite.
The ORP set at 815 keeps the FCL around 1.5-2ppm. I may raise this to get it around 2-3ppm.

I will experiment keeping the pH at 7.8 to avoid the excess baking soda/acid demand.

I appreciate your input!

 

[JamesW]

Your current methods are definitely going to cause some serious problems.

I would keep the TA at maybe 50 to 60 and the pH at 7.9.

I would change to muriatic acid or Carbon dioxide for pH control.

CO2 lowers the pH without affecting the TA and it does not add products like sulfate.

Is the pool indoors or outside?

What is the CYA level?

The ORP set at 815 keeps the FCL around 1.5-2ppm.

Based on this, the CYA must be zero, which means that the pool is probably indoors.

I may raise this to get it around 2-3ppm.

I would go for about 700 to 750 mV.

Are you managing the CSI?

Are you getting CCs?

 

[JamesW]

Our Acid-Rite system is also eating a lot of the acid tablets and lately we go through a couple 45lb buckets a week.

We’ve been discussing possibly moving to muriatic acid because we are getting calcium sulfate scaling.

How many pounds total of sodium bisulfate?

Are the tabs 100% sodium bisulfate?

Where is the calcium sulfate scaling happening?

Can you show what the scale looks like?

 

[DavidLast]

What are the statutory levels required in your state?

 

[DavidLast]

What is the CYA level?

The Becs systems support low or usually no cyanuric, unless there has been a substantial change recently.

 

[DavidLast]

I had some time to think about this situation.

A forum such as this is limited in the information we can provide. In this case, there may be other considerations.

Looking at the information provided, the primary pool chemical donours are both dry. That is calcium hypochlorite by way of Accutab and sodium bisulfate or dry acid as I know it here.

The choice of these chemicals may be because:

• Access to the plant room is restricted, making dry chemicals safer to move on-site.
• Location may make shipping and stocking of wet products difficult.
• Ventilation in the plant room may prevent the use of fuming products.
• Some other local reasons have to do with physical handling, storage, and distance.
• The choice of sodium bisulphate maybe because this acid is viewed to be less aggressive in reducing total alkalinity.

It is difficult to know which of these or perhaps others were the drivers behind the original decision to adopt this method.

In answer to the op question of the TA and the acid rite system dosing flat out, I think I would likely suggest a procedure modification. I am assuming something other than this approach is being taken. I think the best way to proceed would be to isolate the chemical probes, add the sodium bicarbonate, wait a few hours (one complete turnover preferably) then open the chemical probes. I suspect the controller is overshooting when the sodium bicarbonate is added, and this is causing some of the issues.

I have not worked with a BecSys3 for many years as their low tolerance to cyanuric is not great in our market. However, I suspect it is potentially possible to alter the response slope within the controller. This may require the services of a chemical control company. One of the issues I come across is an attempt to adhere to a strict pH target e.g., 7.5. Altering the slope response may be possible and enable a looser approach, allowing a drift between, say, 7.4 and 7.6 rather than an adherence to a strict target. By this I mean the set point is still at 7.5 however the response is shaped so that the pH is allowed to wander a bit further before dosing is ramped up to full speed.

As an aside for any public pool not using cyanuric, I would still suggest testing cyanurate once a month or so. Bathers tend to wear their swimming gear in the pool, take it off, let it dry and use it again. Some may rinse it; some wash it. However, a lot won't. This can transfer the residual chemicals from one pool to another. Cyanuric acid particularly can create problems for the probes with as little as 10 ppm for some controllers and have you chasing an issue that isn’t there. If there is any amount much over 5 ppm of cyanuric in the water, then consider diluting with new water to assist prevent this issue.

I noted a comment in respect of changing the free chlorine residual. Was there a reason for considering this? As I read the local documents I found it is suggesting a limit on the combined chlorine and increasing the free chlorine may increase the combined.

Hope that is helpful.