@CarlD: Liquid Chlorine testing

[CarlD]

Yup, they generally sell it as 12.5 or even 10%. That's to allow for the breakdown. Higher concentrations of chlorine break down faster to lower concentrations. So if they bottle 14% and it breaks down to 12.5% after a few weeks they haven't lied about their product. Still, breakdown is inevitable and unavoidable.

The main reason to test your higher concentration LCs is to see if it has fallen below the rated concentration and then use it up, adjusting your amounts accordingly. I'm not a fan of defending pool stores but in all fairness to them when they are selling gallon jugs of 12.5% and maybe they test at 10 or 11% they aren't cheating you. It's very hard to control it any more than that.

[jhm]

Can you do the same or similar test for MA? The pool store claims they have a much greater strength than Home Depot (which I know a couple years ago the strength was cut in half, but not the price). However, none of the acid I use these day seems as strong as the stuff I was using 5 years ago.

[CarlD]

I have no clue how you would test the concentration of Muriatic Acid. Nor if you can do it with pool tools.

[chem geek]

It should say on the bottle in the list of ingredients the concentration of hydrochloric acid which is typically 31.45% for full-strength Muriatic Acid and is 15% or 16% for half-strength.

1/8th of a teaspoon of 31.45% hydrochloric acid in 1 gallon of water will lower the TA by 81.4 ppm whereas 15% would only lower it by 36.2 ppm. So you could do a TA test of some tap water and add a small amount of acid to see how much the TA gets lowered. You can't test this beyond the amount of TA (i.e. can't measure below zero), but should be able to distinguish between half and full strength. You could add 1/8th of a teaspoon of baking soda to 1 gallon of water which should increase the TA by around 116 ppm if you wanted a larger range to work with. You can use The Pool Calculator to calculate dosages (see the "Effects of adding chemicals" section near the bottom).

Fortunately, the amount that the TA is lowered with acid is independent of starting pH, TA or other parameters so is something you could do using any water source. Essentially, the TA test just adds a chlorine neutralizer, then a dye, and then adds acid so you are just adding the acid in advance to move the TA down before the TA test itself goes the rest of the way until the TA gets to near zero at which point the pH crashes below 4.5 and the dye turns from green to red.

Richard

[jhm]

Thanks, I'll give that test a try. The bottle says 31.5%, but I don't get the strong smells and vapors that used to come with it. It will be an interesting test.