I agree with Hoa101. Also, if you put the ferts in the water at midnight, with all lights out, they just stay in the water until the plants start feeding the next morning. They don't evaporate, or otherwise vanish. Now, if you are trying a lean dosing method, where you try to match your dosing to the plants' demand, it might be a little different. But with EI type dosing it doesn't matter.