Casey,
I'm certainly not an expert but I've recently upgraded my lights.....after months of "study" on this board and elsewhere.....so I think I can get you started in the right direction.
First.....fish don't require any lighting. If you're planning to have a "fish only" (FO) tank, your lighting is only for asthetics. I agree with you, a tank with only "white" lights doesn't look nearly as nice as one with both white and blue actinic lights. Your 75 will probably be 4 feet long so a standard hood will allow 48" normal output (NO) flourescent tubes that will be 40 watts each. Again, if a fo tank, you'd be just fine with one full spectrum bulb (10,000K ) and a blue actinic.
If you want a reef tank, with corals, the plot thickens. Different corals require different/more or less intense light density. Low light coral, like most mushrooms, will need 2 to 4 watts per gallon. Medium light corals are 4 to 6 and the higher light corals 8 or more watts per gallon. Obviously you can't stack enough NO bulbs on top of your tank to get these wattages so you need to consider power compacts (PC), Very high Output flourescents(VHO), or metal halide (MH). All of these require their own fixtures. Some can be combined in a hood. For example, I have a 45 gallon tank that is 3 feet long. I have some corals and want more. I had 3 30 watt NO's......not enough for the corals I want to keep. I upgraded to a hood that has one 175watt 10,000K MH and two 95 watt actinics. I went from 2 watts per gallon to over 8. Not cheap, by any means but the tank looks great and the corals are thriving.
The three different types of lighting I mentioned have different looks as well as different costs, temperature, wattage and size implications. As I mentioned, I like a very blue look. The PC lights, to me, look too white, even with the actinic bulbs, so I knew I didn't want PC's. MH's are very bright and even though the higher K ratings have some blue spectrum light, I wanted more. That's the reason for my combination of MH and VHO.
You can certainly find lots more information about lighting by doing a search on this board.
Jim
