Yea, you could prob just fit a 150W halide on top, but my plants on the side of my 900 long tank bend in towards the center. If you wanna get the BEST lighting, go for two 75W halides. If you can't be bothered with the expense, just go for fluoro's. I wouldn't really recommend the 250W'er cos it'd be too intense in the middle, then leave a few noticable dark patches at the ends of your tank. Rogan has explained everything else really well, so good luck with your tank Quack.