I have 3 nutrafin cannisters on my 55g right now (Don't ask, they were given to me, so it wasn't my money spent on em). I just ordered a pressurized system without a controller. I did get a sms120 ph monitor though with it that has a .01 ph + or minus accuracy. I'm going to move one of the nutrafin's over to my 7 gallon nano. It seems like the controller is more a luxery and not a neccesity. If I find that I need to do more than just have a timer cut off the solenoid for a few hrs I will end up dishing out the cash for a ph controller, though I didn't like that the ph accuracy was plus or minus .2 ph on the sms122. The way I read that is it could be 6.6 in your aquarium and the the probe is reading 6.8. This could add way too much co2 into your system or not enough do to inaccuracy in the probe. I assume most people don't have a problem with it being inaccurate, but I'm still paranoid enough that I would rather take the chance adjusting manually and using a more accurate ph monitor to determine my co2 levels.
i am tossing up the idea whether to add a liquid co2 system to my tank, as you can buy them in small tubes that u manually drip into the tank, or add them to your power head filter through the aerating hole. i think that is correct. As i get more plants, i will see how the liquid fert does, but may end up with the co2. has anyone used liquid co2 before? i didnt see it on the list.