Or buy a meter, and be a little more accurate than any drop kit. all I know is that soil ph testers aren't very accurate, so a meter is usually preferred. it doesn't take much to buy one and a quantitative analysis is ALWAYS better than trying to match up colors. not to mention it's much quicker than drawing a sample, adding drops, swirling, litmus testing, spending the next two minutes trying to figure out which color it's closest to, finding out later that you fucked everything up the first time because your lights put a color wash on the liquid....yada yada