This is a short write up of my DIY low tech CO2 system for a planted aquarium. It has been running for about 2 years now without issue.

Parts list

¼" airline tubing

2X 2 liter bottles

1X 12 ounce bottle

4X ¼" fittings

1X ¼" gang valve

1X bubble counter (optional)

1X diffuser

Equipment List

5/16" drill bit

electric drill

2 part epoxy

Misc. materials needed

Yeast (bakers)

Sugar

Aspirin (optional)

The formula for the yeast mix is simple. I use a pinch of bakers yeast (Red Star in my case) mixed into warm water at 100F to 115F, or roughly hot enough to be uncomfortable but not burn. I’ll let it sit for 5 minutes then stir in ¾ cup of sugar. I’ll then leave it uncovered for about an hour to let he yeast fully activate. I then add ½ of an aspirin (generic of course) and attach the bottle to the system.

The aspirin is optional, but helps keep bacterial blooms in check and allows you a bit more leeway when cleaning the bottles before reuse.

The tubing being used is the cheap airline tubing available at a hardware store. Over time the CO2 and ambient ultraviolet degrades it and it will need to be replaced. I change my tubing out yearly. You can use the more expensive CO2 rated tubing, but as the airline stuff is so cheap the ROI on the higher quality tubing is about 7 years.

I use a cheap gang valve to enable me to pull one bottle from the system while retaining pressure. This keeps the system running while I clean and fill the bottle.

To build the system I’ll first drill a 5/16" hole in the caps for both the 2 liter bottles, and drill 2 5/16" holes in the 12 oz bottle. The ¼" fittings are squeezed into the holes, then potted thoroughly with epoxy. Let them sit and cure for at least 24 hours before use. I find the white epoxy works better than the clear and is more resistant to degrading from exposure.

I use Pepsi bottles as the caps are constructed without a separate seal and have a molded lip used to retain pressure instead. The actual bottle being used isn’t important beyond aesthetics as most can withstand up to 100 psi.

Once the epoxy is dried the system can be set up. Attach a short piece of tubing (3" or so) to the inside of the cap used for the 12 oz. bottle going to the input side. This will act as a trap for vapor and prevent any accident addition of the yeast mixture into the tank. I used an old air diffuser with the stone broken off to weight the end to keep the tubing straight. While this bottle isn't necessary, if your system ever dumps you’ll be glad you have it as it will catch the yeast sugar mixture before it pollutes the tank.

I’d advise filling only one bottle at first, then filling the second the following week. At this point a bottle can be recharged weekly and keep a decent level of CO2 in the system.

I’m using a knock-of glass/ceramic diffuser on my system. Note that it may take a day or three to begin seeing bubbles from this style diffuser. They are made to run on systems of +20 psi and the DIY rigs rarely reach that pressure. Be patient however and you will see bubbles from the diffuser in time.