well, there's lots of factors. one of the biggest is probably your lighting. the higher the light the more need for c02. also the kinds of plants you want to grow, some plants have high c02 demands, while others can grow well without it. in my opinion c02 can benefit any tank, even low light. are you looking at pressurized or diy? pressurized is pretty easy once you get it dialed in. diy on the other hand gets to be a pain for most people after a while, and can be hard to keep stable because the bps drops after the first couple of days. anyway that's my two cents in a nut shell hope it helps. good luck!