Tuesday, August 12, 2008

Compounding Your Own Nutrient

I think I mentioned before that when I first started out doing hydroponics I thought compounding my own nutrient would be really neat. I enjoyed high school and college chemistry. My dad used to tell stories about some of his chemical escapades ranging from making gun powder to creating dots of something like nitro-tri-iodide and putting drops of it on the marble floor near the chemistry lab.
So when I first started I thought, "Gee I can mix chemicals!" But there is a lot of math involved. I thought I'd just give you a touch so you'll have the idea.
Nutrients are given in ppm (parts per million). That sounds a little threatening, but it really only means something like 1 mg (milligram, a thousandth of a gram) mixed into a liter of water (1000 grams of water is a liter). See that wasn't too awful.
It gets a little worse when you have to calculate the ingredients available to the plants when you mix various nutrient compounds into the water. Take Calcium Nitrate (Ca(NO3) 2) as an example. If you want to end up with 100 mg of Ca (Calcium) in the nutrient and you're using Calcium Nitrate you have to add up the atomic weights to get the molecular weight
  • Ca = 40.08
  • N = 14.008, and
  • O = 16.00
But there is only one calcium atom while there are two nitrogen and six oxygen atoms. So the total molecular weight of Ca(NO3)2 is 164.096. So it takes 164 milligrams of calcium nitrate to get 40 mg of Ca and you get 28 mg of nitrogen with it in the nitrate ions. To formulate a total nutrient solution you have to mix a number of water soluble salts into the water in just the right combination and amount. Once you fool around with it a bit you decide if you just want to grow tomatoes that you should leave it to the experts.
I'm always reminded of making a telescope because you want to look at the stars. I had a childhood friend who started doing that and got hooked on making telescopes. The only time he ever looked at the stars was to test his telescopes by looking at double stars.
I need to credit Howard Resh's Hydroponic Food Production for the discussion on calcium nitrate.

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