shine a flashlight or something through the bucket to see if light leeks through. if it does or this is not possible then you can wrap the buckets in a dark colored duct tape or if have the time you can paint them. Could also use Panda film if you have any laying around. Kinda confused on how you can double your grow just by changing buckets, you still only have so many sq ft and must have room to tend plants. Maybe you could shine a light on this??