400 watt MH DIY

[Aquarium_Medics]

A friend of mine was removing some light standards for an aviation fuel station which had a 400 watt sodium light fixture lighting the area. He grabbed the Fixture off the pole and gave iit to me thinking i could use it for my 55 gal reef build. I know i have to disconnect the ignitor for MH bulbs, however, I'm wondering if 400 watts would be too much for a 55 gal, and 2) if 400 is too much could i use a lower wattage bulb in it??

Thanks in advance for any help.