Ive asked the same question.. 3 foot is the maximum for a MH
bulb to cover.. so youll need two for your 55..
the 5 tap ballasts should show multiple voltages.. magnetic ballasts are only designed to be used with one bulb. There are some electronics that are designed for multiple bulbs though..
from my reaserch.. depending on what type of bulb you use.. the ballasts will run you minium around ~$120 for two.. If you want to buy prefab. reflectors.. the best price ive seen on those is $60 for two (I think these can be DIYed by the way).... then the bulbs.. the prices run the gammit performance costs $$ (then again the wrong spectrium can cost $ as well)
Im not positive on how long MH
bulbs last for reef use, Ive gotten multiple answers on that question making this desision tough for me (wether or not to do MH
). If they last on average 3 years say, then the project would be worth ALOT more to me..
I hope this helps..
I would say you would be fine with a pair of 175watt bulbs for clams and sps
... maybe some LPS
on the bottom.. I would shade mushrooms and low light softies with this setup.. just my oppinon though.