You have 4 tanks and are getting 6 more!!!???? I have 5 tanks and I thought I was weird! I want to set up a long tank with a stream for terrestrial and aquatic plant and animal species (ferns, moss, salamanders, turtles, frogs); a tall, brackish, mangrove tank for archer fish complete with a hidden maggot dish to create flies for the archers (it'll have a screened cover!); and another long tank with a beach at one end for fiddler crabs (they dig holes on the beaches of their natural environment) complete with small waves created with the periodic dumping of water by a filter that has that feature built in. I've never used CO2 and like you want to learn more about it so I can use that too, but the $ is an issue right now. In terms of planted tanks, I've mostly had lower light demanding planted tanks which are easy to manage and look great. When you start adding extra light, CO2, and fertilizer a lot more attention is needed to keep the chemistry balanced and to avoid exessive algae growth, but from what I've seen, if you do it right you can have amazing results. I'm curious as to what the differences between your tanks are and what specificly you have in mind. I would immagine that you're creating different environments with different fish in each tank?