For your first one, it's the thrill of the grow, to have fun, to learn things, and maybe you'll even get a little weed out of it.

I would definitely paint the insides with flat white, or put some mylar in there with a non-explosive spray glue. I don't know how much light is absorbed in the tub before reflecting back, but any absorption there should not be. Glossy concentrates light in certain spots instead of diffusing it as flat does.

2 cans of paint - $8
Increase in 1st yield as opposed to now - $16 worth of weed. Exactly.