I'm saying a gallon a month is just a safe bet. You would never run out of room with that rule. And Cervantes may be a crackpot burnout, but he still knows a lot about growing...

And as for the not growing anymore once you change the photoperiod, a pure sativa will keep growing upwards. But if you have more than 30% indica in your blend, you're not going to see dramatic change growing up after a 12/12 switch.

Sorry for the confusion...