Mike, if you test with the 10ml sample, you'll use less of your reagents. BUT, by doing so, you'll only be able to test at .5 ppm resoultion (.2 is more 'accurate' than .5). That being said, .5 is fine IMHO.

PS, when you put the powder in, if it turns pink with one scoop that's all you need to use (save the other scoop for your next test )