What kind of light?

I am growing 8 plants in a deep water system under a 400 watt HPS. I have read that it is ideal to have a Metal Halide (MH) light for the vegetative state and a High Pressure Sodium (HPS) for flowering. Is there anything that I can do nutritionally for my plants during the vegetative state to help offset the light spectrum my HPS lacks?
Eel Ground, New Brunswick

Marijuana, like all green plants, uses light to fuel photosynthesis. So the more useable light the plants receive, the faster they grow. However, the chloroplasts, little organs in the cell where the process takes place, use the red and blue spectrums most efficiently. They don’t use green light and they are fairly inefficient users of yellow and orange light. Unfortunately for plants, both HPS and MH lamps produce most of their light in these spectrums. HPS lamps produce more total useable light than MH lamps. Contrary to what store owners or others will tell you, in controlled experiments HPS lamps outperform either MH lamps alone or mixes of MH and HPS lamps.

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