The very basic do it yourself is take a 2 litre pop bottle, drill small hole in lid and glue in a piece of stiff airline tubing. You connect flexible airline tubing to it and the other end to another piece of stiff tubing that you place in the pickup tube in your power filter. You mix 6 cups water, 3/4 cup sugar, and 1/4 tsp of yeast. Shake well. The yeast puts off co2 as it feeds and multiplys off of the sugar. The co2 will go through the airline, and as it goes through the filter, it breaks up and dissolves into the water. Very inexpensive. I did this to start. Now I have another bottle going into a large tube that a water pump connects to. The water makes a vortex, mixing the co2. The unit was 12.00 total. I'll try and take pics. If you look at the tank pic, the clear tube with the orange lid is what I mean.