The chemical you choose to use will have a major effect on the performance of your pH system, as well as on the cost of maintaining it. But which chemical to use is a matter of trade-offs. One of the most important considerations is safety. Any chemical can be dangerous if it isn’t handled properly — concentrated chemicals the more so. My caution to you is not to lick your fingers or rub your eyes. And please, always wear safety glasses.
The chemical you chose, and its strength, will determine how thoroughly (and how effectively) the chemical mixes with your water and makes the pH change you desire. Too weak a chemical will call for a larger and more expensive feed pump. Too strong a chemical can result in plug flow and a system whose treated pH surges up and down. If you are treating a domestic or potable water, your best bet is still an honest local water treatment professional who guarantees his work. That may still lead you to a pH controller/pump system, but generally only the most difficult of waters would call for that. You can do an inexpensive preliminary check of your water by Jar Testing, where you can get an equipment kit and tester for your water. If you are treating a process water or wastewater, you might start by going to the table on Relative pH Solution Strength.
Which chemical you use will depend upon your particular application and plumbing. Still, you can see that, for example, you would use forty times less of a 50 % sodium hydroxide solution than you would of a 5 % soda ash solution.
Chemical Safe Handling
The stronger solution would let you select a much smaller chemical pump and lower your chemical expense, but it would probably increase your concern over the safe handling of the chemical. And there are sidebars: A pure 50 % sodium hydroxide freezes near 56oF, while a 25 % sodium hydroxide freezes around 33oF. Will your chemical be stored in a heated environment? Or should you look for a chemical vendor who offers a product that contains antifreeze? By the same token, a concentrated sulfuric acid is thirty-six times stronger than acetic acid. Same trade-offs, except that freezing, is not as much of a concern.
Given all the above, we find that many industrial customers balance the safety and expense, and end up using either muriatic acid (18 % hydrochloric acid) or 25 % sodium hydroxide. Customers with trained personnel often opt for concentrated sulfuric acid or 50 % sodium hydroxide. There are exceptions, of course. Some customers are already using an acid or caustic in their plant.
Using the same chemical for their pH system has allowed them to buy in bulk and lower their overall cost. One customer, an apple packer, chose to buy a larger pump and use citric acid to lower their pH. The higher pump expense was easily offset by the deal they got for citric acid from their local apple juice producer. Another customer, in the agriculture business, located a plater with a waste sulfuric acid that he uses as a soil conditioner, in conjunction with irrigation water for fruit orchards. We’ve even had a few fortunate customers whose process chemistry produces both acid and caustic wastes. They store these wastewaters and use them to neutralize each other, with little or no additional chemical.
Whichever chemical, or chemicals, you choose to use for your pH treatment system, you can use the formulas or calculator given in Jar Testing to size your chemical pump(s).