Is all Phenol Red indicator the same?

[ffournier]

I ask this because I have a BioGuard test kit and I'm running out Phenol Red, and it seems BioGuard is out of the test kit business. Pentair sells a 16oz bottle already with chlorine neutralizer in it for $11 and change on Amazon. The concentration of Phenol Red I have is.065%, as stated on the bottle. However I don't see what it is for the Pentair. I use 5 drops of the phenol I have for sample size my kit takes. I'm guessing this is were the concentration of phenol you use makes a difference in accuracy?? So, is all Phenol Red the same?

 

[JohnT]

No, it is specific to the comparator you are using. Also, some has chlorine neutralizer in it to improve accuracy.

 

[jblizzle]

And I can not fathom why you would need 16 oz. It will go bad before you use it all.

 

[chem geek]

You can vary the number of drops to roughly compensate for concentration differences for the comparator you are using and for the water sample size, but the Taylor phenol red is better than most because it contains a proprietary blend of chlorine neutralizers that net out to be closer to pH neutral in their effect. This allows their pH test to be used more reliably up to an FC of 10 ppm.

And as noted in the previous post, organic dyes won't last more than 2 years if kept in a cool place away from sun so there is no point buying a large quantity. Taylor recommends those kind of reagents be replaced every year.