Does your tank have a canopy? If so how tall is it? Normally I would say a 250 watt halide would be the way to go but heat will be an issue with a standard height canopy. Coralife has an aqualight pro retro that is 24" long which would be fine on a 30" long tank. Here's the specs. It was 324 buck from an online vendor. A search using the name should turn up some hits.
24" Aqualight Pro Retrofit Kit 1-150W 10,000K HQI / 2-65W Actinic 03 / 2-1W Lunar Lights (Blue) One 150 watt 10,000KTM double-ended HQI UV shielded metal halide lamp
One external double-ended HQI metal halide ballast with on/off switch, 12-foot lamp cord and 6-foot power cord
Two 65 watt True Actinic 03 Blue square-pin compact fluorescent lamps
One external 2-lamp electronic compact fluorescent ballast with on/off switch, 12-foot lamp cords and 6-foot power cord
Two 1 watt Lunar Blue-Moon-Glow 470nm LED lamps with on/off switch and 12-foot transformer power cord
One external cooling fan - 67 CFM - 34.5dB with on/off switch and 12-foot transformer power cord (4.75" x 4.75" x 1")
Highly-polished reflector (23" x 15" x 3")
Protective glass lens cover
Aqualight Pro Instruction & Installation Guide