Build Carbon Dioxide Reactor for Aquarium

As we all know, plants breathe in Carbon Dioxide and expel Oxygen. Aquatic plants also need this gas dissolved in the water to maintain the biological cycle inside the aquariums.

In an aquarium we add carbon dioxide CO2 for two reasons:

A – To promote the growth of natural plants.

co2 reactor plant

Photosynthesis is a natural process that plants perform. It consists of the manufacture of food using light, from water, mineral salts and carbon dioxide CO2. In this complicated process, oxygen is released into the air or water. It occurs during the day because it is imperative for the sun to be made. In our case, while we have the aquarium on.

Without sunlight or when the aquarium lights go out, plants breathe like most living things by absorbing O2 and expelling CO2. Then they compete for dissolved oxygen in the water. This we should keep in mind as we will see later.

Most aquarium plants need a light intensity of between 0.5 and one w / litre. Increasing the illumination will also increase the need for CO2, so it is advisable to provide it. If you have less than 0.5 w / l you should give up almost all of them. As an example, a standard 60 l aquarium and a 15 w T8 will only have 0.25 w / l. Therefore it is absurd that you add CO2 and even only serve to favor the appearance of the feared seaweed.

A planted aquarium, well lit and with CO2 will delight us with some spectacular plants and will help control algae.

B – To lower Ph.

co2 reactor ph

If we need to reduce a high Ph for our project CO2 is a useful method. When dissolved in water a small part is converted to carbonic acid, enough to lower the pH of the aquarium water between 0.5 and 1.5 points depending on the amount of CO2 we add and Kh. If this is very low the Ph fall can very negatively affect your fish.
Getting CO2 by the “homemade” method is simple and quite cheap unlike the “professional” (metal cylinder, hand reducers, solenoid valve, etc.) much more efficient but very expensive.

Here I show you a tutorial to build a very economical home diffuse.

List of Materials

  • Silicon air hose
  • Rigid airline tubing
  • Gatorade or other flat bottomed fruit drink bottle
  • Ingredients:
  • Bread Yeast
  • Sugar

carbon dioxide reactor building










  • 1/16″ drill bit
  • Hot melt glue gun
  • Assorted measuring cups and spoons
  • Funnel

Unlike many other do it yourself carbon dioxide reactors this one uses a 64 oz fruit juice bottle (the kind Gatorade comes in) instead of a 2-litre pop bottle. A fruit juice bottle has the advantage of a wide, flat bottom making it less likely to fall over and force the contents into the aquarium. Glue from a hot melt glue gun adheres better to a fruit juice bottle cap than the common agricultural policy of a two-litre bottle. The wider mouth makes mixing the solution easier. Finally, the thicker plastic in a fruit juice bottle survives hard impacts better than a two-litre bottle.


Steps to Create Co2 Reactor for Planted Aquarium

1.Take off the Cap

Start by taking the cap off and removing the plastic ring around the bottle’s neck. Occasionally this ring prevents a tight seal especially if caps are used on bottles from different manufacturers. Drill a hole in the cap’s center and slide a 1 1/2 inch length of rigid air tubing through the hole. With the hot melt glue gun, glue the tubing in place. Use liberal amounts of glue on both the cap’s inside and outside. Be careful not to block the rigid air tubing. Pressure from the fermentation process will build up over time and will rupture the plastic or glue seal spraying the bottle’s sticky and foul smelling contents. Leave only a short length of rigid tubing inside the cap to prevent the bottle’s contents from being forced into the tube and then the aquarium. After the glue sets, screw the bottle’s cap back on and blow into the tube. No air should escape. If a hole is detected, peel the glue away and start again. Layering more glue will probably not fix the problem and could block the tube.

2. Fill the Bottle

Take off the cap and fill the bottle with lukewarm water to two inches from the rim. Use filtered water or add an aquarium tap water conditioner to rid the water of chemicals capable of killing the yeast. Add two cups of sugar to the bottle and mix thoroughly until the sugar is dissolved. Add 1/8 teaspoon of yeast to the solution and mix thoroughly until the yeast is dissolved. This amount of yeast is adequate to keep smaller aquariums (up to 30 gallons) supplied with CO2 for approximately two weeks. A larger aquarium (up to 55 gallons) requires 1/4 to 1/2 teaspoon but be prepared to change the bottle weekly to avoid a drop off in CO2 levels. For a planted aquarium larger than 55, two or more containers can be used, but the purchase of a commercial CO2 tank and regulator system should be considered.

3. Connect Silicon Air Hose

Connect about a foot of silicon air hose to the rigid air tube. Connect the other end to the check valve. Make sure the check valve is oriented in the correct direction. If the flow direction is not marked on the device, blow through one end to determine the proper direction of flow. The check valve is used to keep aquarium water from syphoning back into the bottle. If this happens, the pressure from the later fermentation of CO2 will build up and force the bottle’s contents into the aquarium. A check valve is not necessary if the bottle is kept in the aquarium.

4.Cut Air Hose

Cut enough air hose to reach the power head and insert the hose into the power head’s air intake hole. The CO2 bubbles are dispersed by the powerhead’s current forcing CO2 to dissolve into the aquarium. The hose can also be fed into a canister filter’s intake. However, the filter tends to run noisy due to the gas rattling around the impeller and on occasion may stop the filter from working altogether. Another advantage of a power head over a canister filter is the ability to count the solution is producing the rate bubbles. If the rate begins to slow, a new batch is needed.
Use the second bottle to mix a new batch of yeast and water solution. Let the solution sit for 24 hours before exchanging bottles to give the yeast adequate time to produce a steady quantity of CO2, thereby avoiding fluctuating CO2 levels in the aquarium. CO2 levels directly affect water’s Ph and rapid or severe shifts in Ph adversely affect aquatic life.

Word of caution: This method of introducing Carbon Dioxide into the aquarium cannot be precisely controlled and will cause Ph fluctuations. The softer the water, the worse these fluctuations become. Use this method only with relatively hard water, as this will buffer fluctuations in Ph. If softer water is used, experiment first with a fishless aquatic garden until the changes in water parameters are understood.

Photo Research Help, All credit goes to The Smart Weightloss  team for researching the content photos

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