IMO a 150w mh would be perfect for that size tank. A ROIII pendant would fit nicely over a 18" tank. A couple of well placed fans should prevent any heat issues. It sounds like it will be a cool little tank. Good luck!
so if i am going for a MH should i get 6500k or 20k and what model should i get currently i am having a 150W DE with 6500k iwaski bulb. sould i cont to use it with blue light together ??