I noticed that you can test at the 10ml at 0.5 per drop or the 25 ml at 0.2 per drop. Is there any reason to use one vs the other. With high chlorine levels I was using the 10ml just b/c it took less reagent to get a reading but this morning I tested twice and got 2 different readings. With the 10ml sample I got 11.5 and with the 25ml I got 9.5. What would cause such different readings? Which one is more likely to be right?

Thanks!