jus buy a 24 in fixture alot cheapier goes rght over the tank wit the open space it helps vent and u could do a fan if need b i have 2 setups like that wit 2 different fixtures 1 is a 150 mh wit leds and other is a 4 bulb t5 both tanks doin great
Look for a used current 20" sunpod either 150w or 250w version, I say used cause they stopped making the sunpod which is an AWESOME little fixture. I had the 250w model on my 24g nano cube and was able to keep and grow just about anything, I since upgraded to a 45g cube and I'm still using the same light.