For many years there has been a misunderstanding in the swimming pool service industry about the chemical differences between using soda ash (sodium carbonate) versus bicarb (baking soda or sodium bicarbonate) to adjust pH and alkalinity in swimming pool water.The misinformation being taught in some seminars varies. Some seminar instructors claim that soda ash and bicarb, pound for pound, add equal amounts of alkalinity to pool water while raising the pH differently; while others claim that bicarbonate actually increases the alkalinity more than soda ash! Another inaccurate claim is that sodium bicarbonate will always increase the pH somewhat.SODIUM BICARBONATEA 1% solution of sodium bicarbonate in water has a pH of 8.4. Therefore, when bicarbonate is added to water having a pH less than 8.4, it will cause the pH to rise towards 8.4. Conversely, and what is not understood by some, is that if the water’s pH is greater or higher than 8.4 (which does occur occasionally in swimming pools), adding bicarbonate to this water will slightly decrease the pH down, towards 8.4. This means that in new plaster pools, when the pH often soars to very high levels, adding both acid and bicarbonate will reduce the high pH found in these new pools. By adding bicarb with acid, the alkalinity can be kept at appropriate levels, and balancing after startup will be quicker and easier. If the alkalinity is already high in a new pool, then only acid is needed to lower pH – which also lowers the alkalinity.In general, adding sodium bicarbonate will not affect the pH significantly, since the starting pH is not significantly distant from 8.4 to begin with. However, the further the pH of the water is from 8.4 to begin with, the more effect bicarb will have on shifting the pH. More importantly, the amount and the type of total alkalinity present in the water will also determine the amount of pH change when bicarbonate is added to water. The rule here is that when total alkalinity is low, it will have a greater effect on the pH from the addition of sodium bicarbonate. For example, if sodium bicarbonate is added to one pool that has a pH of 7.0 and an alkalinity of 20 ppm, and also added to another pool that has a pH of 7.0 but with an alkalinity of 100 ppm, then the greater pH increase will result with the pool that has alkalinity of 20 ppm. This is due to the greater pH buffering (resistance) of water with higher amounts of alkalinity.SODA ASHA 1% solution of soda ash in water has a pH of approximately 11.4. Because of this high pH condition, soda ash will raise the pH in water more significantly than will sodium bicarbonate. And just as with bicarbonate, soda ash will also more significantly increase the pH when a lower alkalinity level exists in the water because of the lack of sufficient buffer.Contrary to some information, soda ash also adds more alkalinity than bicarb. The amount of alkalinity contributed by soda ash is about 58.5% more than sodium bicarbonate, or in other words sodium bicarbonate is only about 63% as strong as soda ash in terms of increasing alkalinity.So what does all of this mean? Well, first it means that if you only need to raise alkalinity but the pH is okay, it is better to add bicarb because it will contribute the alkalinity needed without affecting the pH very much. If you need to raise the pH but the alkalinity is okay, then adding soda ash is best. But don’t assume that the alkalinity won’t go up, it will. You just hope the alkalinity won’t go up too much. Generally, do not add more than 4 pounds at a time per 20,000 gallons.And if you need to raise both the pH and alkalinity, then pound for pound you get more “bang for your buck” with soda ash, and it is cheaper too. But be careful. Adding too much soda ash will often cause the precipitation of calcium carbonate which results in cloudy water.
Not sure what part of the country you are from, and glad to hear it is being correctly taught. But I have attended a few seminars where it has been incorrectly taught. Also, I have taught seminars in several different areas where service techs have had a misconception regarding soda ash and bicarb. Sometimes, it is only a matter of a miscommication or misintrepretation. You have it right, and your comment is duly noted and appreciated.
I've been attending seminars at pool shows for a long, long time, and your conclusion - use baking soda to raise Total Alkalinity and soda ash to raise pH - is the same as I've always been taught.
Honestly, I don't think I've ever heard anyone assert that, pound for pound, baking soda and soda ash will raise alkalinity an equal amount. And I don't think I've ever heard that because it wasn't really germane to the topic.
I think it's generally understood that you use soda ash in much smaller quantities than you do baking soda, and so the typical addition of baking soda will have a more dramatic effect on TA because you normally add so much more of it, not because the lecturer was claiming a pound for pound equivalence.
It's misleading to start out your article with the premise that you're here to correct a widely held misimpression, when the conclusion you draw is the widely held industry standard.
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Honestly, I don't think I've ever heard anyone assert that, pound for pound, baking soda and soda ash will raise alkalinity an equal amount. And I don't think I've ever heard that because it wasn't really germane to the topic.
I think it's generally understood that you use soda ash in much smaller quantities than you do baking soda, and so the typical addition of baking soda will have a more dramatic effect on TA because you normally add so much more of it, not because the lecturer was claiming a pound for pound equivalence.
It's misleading to start out your article with the premise that you're here to correct a widely held misimpression, when the conclusion you draw is the widely held industry standard.