I use 3 250W HQIs on mine, and 2 VHO actinics. MHs are PFO ballast and pendants, VHOs run off of an Ice Cap Electronic ballast.
Some people will say you need 400W MH because the 180 is typically 24" deep, but the HQI's give off more light than standard 250W MH bulbs, and you can vary your coral placement based on lighting needs.