Blue and actinic lamps will make the glow you're talking about. 2 Blue + lamps and 2 actinics will make the light very blue and make a lot of that nuclear glow you're looking for. Retrofits are simply kits that consist of the individual parts--ballast, bulbs, endcaps. You have to make a way to mount them. Tons of options available to do that. Mount them to wood, metal, canopy, suspend them, etc. I think a fixture would be too clumsy on your tank, along with the halide.I just want the colors of the corals to look like theyre basically glowing kind of like neon ya know? im looking for whatever would work best for my set up which you guys know all to well by now! i dk what a retrofit is haha