Two Hydroponic Tomato Questions:
 

Hi, I'm new to growing hydroponic tomatoes and have a couple of questions I'm hoping somebody can help me answer?

1)what EC/TDS/PH do you run your tomatoes at?

2) My multi-testing meter has an ORP, or oxygen reduction potential reading. How is that relevant to my grow? Is it a useful number for hydropoinics or irrelevant?

My Blog:
The Greene Tomato

Because plants take up nutrients in a pH range, and conditions will affect the perfect pH, it's better to shout for a range rather than a specif number. I try to keep mine at about 6.0 because it's in right in the middle of the generally recommended range of 5.5 to 6.5, fluctuation wont be much of a problem. I don't use a meter for EC or TDS, but the EC should be in the range of 2.0-5.0. Both EC and TDS just gives you an idea of the strength of the solution, but doesn't tell you what elements are being used up faster than the others. By simply adding more nutrients to the solution to get it in range, the nutrients that were not used by the plants could reach high concentrations and cause nutrient lockout. That's why it's better to just change them, but the meters can tell you how fast they are being used up in general.
To be honest I never herd that term before, but I did a quick search for oxygen reduction potential I am not positive but It seems that it is related to the dissolved oxygen levels of the nutrient solution. I personally feel you can probably never have too much oxygen at the root system. A number of things can affect oxygen in the nutrient solution, but I would add about 1 tsp (5mL) of hydrogen peroxide (H202) per gallon to the nutrient solution. That will add oxygen molecules to the nutrient solution without hurting the plants, check the readings both before and after and see if it rises. I add hydrogen peroxide to my nutrient solutions at 5mL regularly, about once a week but I don't have a meter to tell what the levels are.