hoppycalif

I have been reading about the indicator used in Aquarium Pharmaceuticals pH test kit - bromothymol blue. As far as I can find out, it isn't critical how much of the reagent you add to the test sample. The color should stay the same even if you add another drop or two. Does anyone do this? It would seem to make telling the colors apart much easier. The reason I wonder if this would be acceptable is that the reagent contains sodium hydroxide as well as the indicator, and intuitively I think that means the actual pH of the test sample comes partly from the reagent, so the three drops is the only accurate amount that can be used. Any comments by the non-chemistry challenged among us?

hoppycalif

I did some testing today. I checked two identical samples of water from my aquarium, from the tap, and a mixture from each, to get 3 different pH's. One of each pair was done with the 3 drops of reagent, per the instructions, and the other with 6 drops. My goal is to intensify the colors to make reading the pH easier. From the photos below, you can see that it made very little difference, and the pH would read the same in either case. In each photo the 6 drop sample is on the right.


This one is a flash photo - tap water.


The same samples with natural light.


Fish tank water.


Mix of tap and fish tank water.