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Alkalinity above 500 ppm and pH 8.4 - Swimming Pool Help

Alkalinity above 500 ppm and pH 8.4

Problems relating to pH and total alkalinity. Increase ph, increase TA. Reduce pH, reduce TA. pH chemistry advice and techniques.

Alkalinity above 500 ppm and pH 8.4

Postby njadeja » Fri 01 Jun, 2012 03:41

I have pool above 100K gallon. My Alkalinity is above 500 and pH is 8.4, Calcilum hardness is 60 ppm. I am trying to add continuous load of HCL as prescribed but due to filter, back wash and adding new water which is of 7.8 pH I am not able to lower TA. What should I do?
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Alkalinity above 500 ppm and pH 8.4

Postby chem geek » Sun 03 Jun, 2012 02:57

I presume you are concerned because the pH tends to rise fairly quickly due to the high TA level and if you also have high CH then you have a risk of scaling.

The only way to lower the TA, other than using reverse osmosis (which you can check to see if it's available in your area -- it would reduce CH as well), is to add acid and aerate the water. Use Muriatic Acid since you'll need a lot of it and it doesn't add sulfates to the water. See the procedure in this post. It will take a lot of acid for your pool since 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons to lower the TA by 10 ppm. So with a 100,000 gallon pool, that's 2 gallons of acid to lower the TA by 10 ppm. You can add more than that amount since you can get down to a pH of 7.0 initially, as per the procedure. Just make sure to add it slowly over a return flow in the deep end with the pump running and then lightly brush the side and bottom of the pool where you added it to ensure thorough mixing.

You can use The Pool Calculator to calculate rough dosing for lowering the pH (which also lowers the TA -- aerating the water then raises the pH without changing the TA).
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Alkalinity above 500 ppm and pH 8.4

Postby SgtBilko » Sat 29 Dec, 2012 13:07

I have a similar problem (TA 500 +) although a much smaller pool in a 67500L (about 15K gallons).

It looks like I'm going to need 7.5 Gallons of full strength Muriatic Acid to get down to 250 ppm

Are there any safety concerns over pouring that amount of acid into a swimming pool ? I don't mean handling issues or making sure it is poured in slowly. I mean long term issues for bathers

Thank you
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Alkalinity above 500 ppm and pH 8.4

Postby chem geek » Sat 29 Dec, 2012 16:12

The acid will lower both the pH and the TA so if you add too much acid too quickly then you will get the pH too low and that will be a problem for bathers (stinging eyes) and will degrade pool plaster and can harm pool equipment. This is why the procedure to Reduce Total Alkalinity Levels has one lower the pH only to around 7.0 or 7.2 and then uses aeration to more quickly drive off carbon dioxide from the pool.

The only net result from the procedure other than a lower TA is a higher chloride level as a result from the acid. This is not a problem.

By the way, you'll likely need to get your TA below 250 ppm. Depending on your source of chlorine, your TA may need to be as low as 70 ppm for pH stability when using hypochlorite sources of chlorine in a pool with waterfalls, spillovers, fountains, etc. or it may be OK at 120 or 140 ppm if you are using Trichlor (but that has other issues of building up the Cyanuric Acid level).
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Alkalinity above 500 ppm and pH 8.4

Postby SgtBilko » Sun 30 Dec, 2012 04:11

Thanks

What level do you think is appropriate if I am using Bromine ?
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Alkalinity above 500 ppm and pH 8.4

Postby chem geek » Sun 30 Dec, 2012 04:25

Basically, whatever level that has your pH be fairly stable. If your pH tends to rise over time, then lower the TA. If it tends to fall, then raise the TA.

Once you find the TA sweet spot for reasonable pH stability, then you can adjust pH and especially CH as appropriate to have the saturation index be near zero, if you have a plaster pool.
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Alkalinity above 500 ppm and pH 8.4

Postby SgtBilko » Sun 30 Dec, 2012 04:29

Thank you
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