Reef Chemistry Question of the Day #204 Alkalinity Testing

[Randy Holmes-Farley]

My issue is a minor one with the wording. I would rephrase it to be something like (my edit in italics), "There is a dye in the test that can bind to a proton (H+) when enough protons are present in solution, and which gives a different color when bound in that way. You add acid (H+), which converts the dye to a different color. When you have added enough H+ to leave enough free H+ after reacting with the carbonate and bicarbonate to bind to a sufficient number of the dye molecules, the color changes and you are done." You may have considered my edit to be implied, but I think it should be elaborated.

Thanks, Jim. Yes, It was implied.

 

[Hans-Werner]

It is a surprisingly difficult thing to pin down exactly, for reasons I'm not sure of. I'd aim for 4.2 or a bit higher.

I think the alkalinity or KH in °dH is derived from the acid capacity to pH 4.3. Traditionally it was determined with methyl orange and hydrochlorid acid.