Injecting Soda Ash to Increase pH
The chemical name for soda ash is sodium carbonate, chemical formula Na2CO3. It is more basic, that is, less acidic, than sodium bicarbonate (baking soda), whose chemical formula is NaHCO3. The purpose of sodium carbonate is simply to increase pH.
Its use in water treatment is to increase the pH of acidic waters. The trick is how to do it and how much to use. Below are some suggestions and comments from a variety of sources.
From Pure Water Products
Mixing Soda Ash with water and feeding it with a pump to increase pH is a trial and error procedure. It's best to start with a small amount of your mixture so that you can make alterations as needed.
The amounts below are a suggestion made by one source:
Mix 2 lbs of Soda Ash with 5 gallons of water. Set your pump at 50% or 60% capacity. Let the unit run for a time, and use water as you normally would, then check the pH a few feet downstream from the injection point. If the pH isn't where you want it, make adjustments.
Adjustment can be made by adding Soda Ash, by adding water, or by adjusting the pump up or down. Keep adjusting until you get the pH exactly where you want it.
Be sure to keep records, and keep in mind if the solution gets too strong, you may have to dump your mix and start over.
If you aren't able to get the pH as high as you want it, you may have to switch to Caustic Soda.
Caustic Soda is about 30% stronger than Soda Ash. Ten pounds of Soda Ash in 20 gallons of water is equal to approximately 7.5 lbs. of Caustic Soda in ten gallons of water.
Caustic Soda is available in pool supply stores. It's trickier to use than Soda Ash, so proceed with caution.
Here are some helpful facts about Soda Ash injection:
1. 0.926 lbs. of soda ash mixed with one gallon of water makes a solution of 10% Soda Ash.
2. A 10% soda ash solution is 100,000 parts per million soda ash.
3. It is common to inject between 50 and 500 ppm soda ash to increase the pH of well water. The amount you inject depends on how much you need to raise the pH. It is a process that usually involves some trial and error.
More about Soda Ash from various sources:
The amount of soda ash needed is actually determined by the amount of CO2 in the water being treated, and since this is seldom known, trial and error is the normal procedure.
According to a WQA publication, “For each ppm of carbon dioxide in the water, 2.5 ppm of soda ash is needed for neutralization. If caustic soda were used, only 0.85 ppm would be needed to neutralize 1.0 ppm of CO2.”
“Often a starting solution dosage of four ounces of [of soda ash] per gallon of water is used.”
“[Where disinfection is needed], it is possible to feed a mixture of hypochlorite/soda ash simultaneously for dual treatment.”
A Soda Ash manufacturer’s statement on solubility:
Soda ash dissolves readily in water to give a clear solution, however, it exhibits an unusual characteristic in that maximum solubility is at the low temperature of 97ºF. At that point, a saturated solution contains 33.2% Na2CO3 by weight. A 10% by weight soda ash solution is saturated at 49ºF. It is recommended that a 30% by weight soda ash solution be stored at 120ºF.