Hello, New guy here. I recently set up a 75 gallon fresh water tank to keep our pond gold fish in for the winter, we live in Michigan. I have purchased lots of live plants and we currently have about 20 fish in the tank. I have seen advertised a c02 diffuser and I wonder what this is. How do I know if i need one as I dont like to waste money? Can you offer any tips that will help me cut down on how much time I have to spend attending to this tank? Thanks for your help. KP RTFD