Isabella has done a hellofa fine job with the EC meter project. Havent built it yet but sure it works as well as comercial units. Been thinking of doing something like this for a while and she has saved me a lot of research. It would be interesting to leave the electrodes active all the time and use a microcontroller (PIC) to log the nute concentration so as to find the optimum grow parameters.
Unfortunately her work on thePh meter wasnt finished but a cheap hand held unit will do. Seems that the ideal Ph is already known.
Anyone else interested in this ?

EC/TDS/PPM Meter

Cheepo pH Meter