Screwauger hasn't been around for a while to answer. By the look of it I'd say 15ltr pot. 2 x 15ltr will kill it in a 3x3. If you're eu side and don't want to get messed up in mixing nutes, use AutoPots with BioTabs. Only add water from the res... too easy.
So I fucked up and bought 4 Pot XL system for a 3x3x6, will my auto grows be too large for my tent to handle?1 or 2 15ltr. Not the XL but then I already answered that here:
I think you should go with two plants only unless you do strains known to stay small. My growdrobe was ~9 sq. ft., and fitting more than 2 mephisto CQ's in there would have been tough. And CQ's are not xl size. A really big strain would have meant only one plant would fit.Wondering what people think about 1 XL Auotopot or 2 of the 15L Autopots in a 3x3 tent.