I'm trying to develop an assay to detect IAA from bacteria and I'm finding that the Salkowski's reagent dissolves agar/agarose. My first thought is to dilute the acid out and maintain the FeCl3 concentration. I was curious to know if any clever chemists were familiar with the complexes this forms when it reacts with indole compounds like IAA to make a pink/red color. Some initial tests are showing that I can dilute the acid almost 10-fold and still get a very similar reaction.