Best equipment for testing chem nuts ppm?

No I'm not talking about a TDS/EC reader. I'm more interested in what you guys are using, if any, for individual chemical tests, within your nutrients (e.g. Colourimeters, ect.)

@churchhaze...

You could use ion selective electrodes (very expensive). You could use a colorimeter, but you'd need to understand the chemistries involved for each thing you're looking for which could take a long time, and requires chemists to setup the tests.

Personally, I am not using any of this. When making DIY nutes, I know pretty well how much of each chemical goes into each stock solutions by the scales measurements. (ion selective electrodes would be fun to play with, but I just have an EC meter)