Would someone please explain the acid demand test?

[Sjde]

I have tested pH with a color matching system and then just guessed at the amount of baking soda needed to raise pH (seems I rarely have to lower it or alkalinity), starting low with the amount listed on the container.
But my new drop kit test also has an Acid Demand Test (used when you need to decrease pH I think?) and a Base Demand Test (to raise pH). I tested on my home drinking water first and it showed a pH of 8. So I used the solution for the Acid Demand Test and it took only 1 drop to change the color to what it should be. But my instructions say nothing about what to do after that. I thought there would be instructions about how much to add based on how many drops it took. What is the purpose of this test?

 

[jblizzle]

There should be a table stating what you would need to add based on the number of drops.
But, you can use Pool Math to tell you what you need to add to reach a target too, so there is not too much value to those demand tests in my mind.
I am keeping my pH up near 8 recently around which everything looks pink. So I use the acid demand drops to get a qualitative feel for how high the pH is. If it only takes 1 to get some orange tint, then I think I am pretty good, but if it takes a few, then my pH might be pushing 8.2 or higher.

 

[jblizzle]

How are you chlorinating? With all the aeration in a spa, the pH should tend to rise up and you should likely never need to add baking soda. OH, and baking soda is not the proper chemical to raise the pH, it is used to raise the TA. See Recommended Pool Chemicals

 

[Sjde]

I didn't see a table but I'll look again.
I use bromine . And have been using Spa Up which is baking soda and says to use to raise pH and Alkalinity. No?

 

[Sjde]

So pH is better raised with soda ash (sodium carbonate) but it comes in a 15 lb bucket for $40. I know I can use borax too, but will I know how much? Pool math may say but that is for using bleach, not bromine. (I don't want to use chlorine or bleach at a spa in a vacation rental. ) Plus there is no choice for an acrylic shell.

 

[jblizzle]

Adjusting levels like pH is not dependent on if you are using chlorine or bromine.
Use fiberglass.

I did not look it up, but Spa Up could be a combo of powders. Or they are relying on the higher TA to pull the pH up (which in general is true), but the higher you make the TA, the faster and higher the pH will want to rise. Which is usually opposite of what we want to happen.

 

[Sjde]

“Adjusting levels like pH is not dependent on if you are using chlorine or bromine.”

Yes , I realize that.

Spa Up is pure baking soda. And I have wondered with using this product , how you raise one without raising the other if that is not what you want.

 

[jblizzle]

You seemed to indicate that you could not adjust chemistry levels using Pool Math just because you use bromine. I just wanted to make sure you realized the only thing that would be different would be the chlorine / bromine adjustments.

You can use Pool Math to show you the impacts of adding baking soda or soda ash. The first will raise the TA with little impact on the pH. The 2nd will raise the pH with little impact on the TA.

Having a higher pH will not affect the TA; but having a higher TA will make the pH naturally rise faster.