Most use a sunpod. But I thought that I read it was 16.5 in not sure though. Look at demartini's tank. Hers is great and uses it. I on the other hand like the stock look of a hood. I just started wiring up the new ballast and stuff this morning to add a 70watt mh to my 24 gall nano hood. along with one 32 watt actinic 03 pc bulb. alot of work to be done but the ones i have seen look really nice. Just a thought. I am also adding 2 more high volume fans to keep temps down. Good luck with your lights !!!