What are the dimensions?
Two 250 W MH fixtures with good bulbs, reflectors, and ballasts should provide a lot of light, and would be fine. I have a Lumen Max 2 pendant that I like. It's a newer product from the makers of the Reef Optix pendants. There's an equivalent product from Lumenarc, and some reflectors separately available as well.
Lots of animals would be happy with less light, and some 175 W bulbs would be fine, as well.