if memory serves me, cannabis uses a lot of phosphorus, which is the middle nutrient on fertilizers. The first is nitrogen and the third is potassium. I got a bottle of super-concentrated Schultz 10-15-10 fertilizer with lots of micronutrients at home depot, and it was like $4. It says to use 7 drops per quart of water, and i have about half a pint of the stuff. good luck!

um, wait, are you using hydroponics (as opposed to soil) with no nutrients?! cause that's a huge no-no.