Please see post #3 in this thread: http://www.poolforum.com/pf2/showthr...bined-chlorine

If you have measurable CCs, that is 0.5 ppm or more in a 10 ml sample, the solution will turn pink immediately. You could try to test on a 25 ml sample which increments at 0.2 ppm but you'll use more reagents and won't really gain any significant information.