5 watts per gallon on a 250 gallon tank is WAY too much light. Unless it's going to be a reef tank. At most on a tank that size you might need 2.5-3.0 wpg. One thing to remember is the MH bulbs are expensive and have a short life span. Consider that you are going to have to replace bulbs every 18 months or so with the MH lights. Consider that you can pretty much run the PC bulbs till they die. Consider the fact that you are shooting for way too much light. Now figure out the actual starting costs and then the Total Cost of Ownership.
I can tell you that I would start with 384 watts (4x96 PC) and then if I needed more I would add another 192 watts (2x96) watts.
The watt per gallon rule really breaks down on tanks this size. And it breaks really low.
If you have your heart set on MH lights then I would recommend 3x175, or maybe 2x175 and 1x250 at the most. Run the 175s on the sides and the 250 in the middle. |