Any alternative fighting my 480ppm TA fill water?

JohnT · Jun 27, 2012

We are having an extreme drought combined with unusually low humidity, wind and extreme heat this year. I'm losing a lot of water to evaporation, and consequently having to add a lot of water. Problem is my well water TA is 480ppm, and I'm having to add a lot of acid to keep pH under control.

Any way I could pre-treat the water to make things easier? I was thinking of filling my 400 gallon farm tank with water and adding muriatic acid to drop the pH well below the level required to outgas CO2 and spray the water through a nozzle into the pool. Or could I mix them as I sprayed some way?

JasonLion · Jun 27, 2012

Filling a tank about 3/4rds full, adding lots of acid, and aerating would be a good pre-treatment. That does require a separate aeration system for the tank and some kind of transfer pump to get the processed water into the pool, but that shouldn't be too difficult.

JamesW · Jun 27, 2012

RO would work, but might be too expensive.

Can you give more detail about this?

Information such as all chemical levels, how much fill water you add at a time and how often, what the fill water does to the pH and TA, how much acid is added etc.

I think that as long as you can keep the CSI under control, there should not be too much to worry about. Adding borates would make things easier. Using a solar cover would also help.

Do you have another source of water?

rclifton · Jun 28, 2012

Think I'll keep checking back in this thread as I could use the same kind of help. My fill water has a TA over 600 and I'm losing about 1" to 1.5" of water daily... I've got the TA down to 190 in the pool but it seems to be a battle at this point between how quick I can get the PH up to add more acid and how much fill water I have to add every day..

Sorry I couldn't help Op.. Hopefully someone has some good ideas...

JohnT · Jun 28, 2012

After some reading, I came across a statement that alkalinity varies with pH from 5.0 to 8.0. At 8.0, the TA is at its max value with no CO2, while at 5.0 the TA is zero and all of the carbonate is converted to carbon dioxide.

With pool chemistry in mind, a pH of 5 is a little scary, but rainwater tends to have a pH around 5.6 and can get down around 5, so it seems that reducing the pH of a tank of water to 5, then aerating with a nozzle as the water is pumped into the pool MIGHT let me get the TA out of the water quickly. This wouldn't be hard to try on a smaller scale.

The question is, if I spray the water in a coarse mist, can I get rid of all or most of the CO2 from the water before it hits the pool?

JasonLion · Jun 28, 2012

That very much depends on how fine a mist your sprayer produces.

chem geek · Jun 28, 2012

Lower pH has the carbon dioxide outgas significantly faster because it moves more of the carbonates to aqueous carbon dioxide. See this chart where you can see how far out-of-equilibrium the carbon dioxide in water is compared to air. Remember that 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons lowers the TA by 10 ppm.

480 ppm TA even at pH 7.5 has around 50 times more carbon dioxide than air. At pH 7.0 it's 166 times. At pH 6.0 it's 1638 times. At pH 5.0 it's 14,484 times. In practice, you won't be able to get the pH that low unless you add enough acid to exhaust much of the TA. So in a tank with no calcium carbonate (i.e. no plaster or grout in tile) you could readily add as much acid as you know you need to get the TA down to where you want (say 80 ppm) and then aerate to get the pH back up. Just note that as you get higher in pH, the rate of pH rise will slow down -- probably getting much slower as you get to 7.0 to 7.2 or so.

Obviously, you would never do this technique in a pool itself because you'd risk dissolving the plaster or exposing the equipment to low pH that could accelerate corrosion.