would a 70 watt mh 20k light work on a 20L or 150? I dont want to over do it. right now i have 300 watts of vho (150actinic and 150 watt 50/50) and im looking to replace that.
i remember reading a post that someone had a 70MH on a 10gal. bother tanks have the same height. you would just have more light in the center. they chose the 70MH cause it produces less heat, but that could easly be fixed with some fans. i have just one fan on my refugium, that goes on during the day. i havent had any overheating problems yet.
I would say 150 just b/c I have a 70 over my minibow now. I think the 150 will have heat issues but like he said it can be figured out. you can also use your atinic lights for a blue look.
I would also second everyones opinion and say go with the 150. More light gives you more options and 150w of MH over a 20l definitely isn't too much. Especially since you are replacing 300w of VHO. Are you completely discarding the VHO or just taking out some of the VHO's and leaving a few for actinic supplimentation?