Q:

nutrient sensors for hydrophonics with raspberry

I am the happy owner of a mancave and I've decided to invest in raspberries, sensors and some small hydroponics vaxer from ikea. I've gotten a camera and some temperature sensors which can log pictures and temperatures/humidity to the cloud. 
A next step would be to measure the nutrients in my hydrophonic system as well. I'm having trouble finding proper sensors for it though. I'm interested in hearing of any sensors that might be applicable for a hobby project or what the possibilities might be. Any experience or references are also welcome. 

A:

You need a TDS (Total Dissolved Solids) meter (aka EC/PPM meter) for measuring the nutrient content in your water, and you should also have a pH meter for maintaining a proper alkaline/acid level.
I did a quick search, and here's a link for each of the above meters, and how to integrate them to the RPi. They are brand-specific, so you'll have to do your own searching if you seek out alternate units:
TDS meter
pH meter
Note that I am not making a recommendation for the above products whatsoever. I've never used them; they are just examples of what you're going to need.

