I have 1 Wet and dry filter . The black stuffs inside the filter are black sponge and black carbon. one Co2 20 lb tank . This Co2 tank last more than a year and it is still going at 2 bubble a second with timer. The plant does not takes Co2 at night ,so I set the timer. It only turns on Co2 when the light on. This way it save a lot of Co2, 8 T8 48"lights, one heater I hied in the wet and dry filter, one 25W UV light.
I change water 10% use it for watering my plants one a week, suck the mud at the bottom of the tank 1 every 2 or 3 weeks and change Cotton in the filter whenever it turn black. The sponge I just leave it alone.