The size of the container doesnt change because of the growing medium being perlite. I prefer growing in 2 gal containers, but that is just a personal preference. I also do 100% perlite and find it very simple. As for the cal-mag....I use it at 1/2 strength with every feeding, I mix my nutes up in 1 gallon jugs. I dont start using cal-mag until the plant shows signs of a calcium deficiency (usually brown on the leaves). Hope this helps ~Bone