carbon dioxide in the Aquarium

Carbon dioxide use in the aquarium is widely misunderstood by many aspiring hobbyists. Many plants require the higher levels of Co2 for optimum growth because it helps them to take up other nutrients more efficiently also.

Fast growth isn’t the only advantage of carbon dioxide injection. When supplied, plants will exhibit thicker stems, have better colour and show less deficiencies and your aquarium and will have less algae growth.

Most plants grown in the aquarium(submersed) can also grow outside(emersed). When grown emersed the plants have access to the atmospheric co2. In the home aquarium though, the co2 levels are quite low. Plants in non co2 injected aquariums are more reliant on Nitrogen(N), Phosphorus(P) and Potassium(K) and often will show co2 deficiency. As plants are mostly made of carbon it makes sense that supplying them with optimal amounts. This will as a result, equal faster and healthier growth. In a natural submersed environment the co2 levels are quite high because of decomposing organics. Well above the optimal 30ppm.

Gear Required For Co2 Injection.

  • Co2 Cylinder. In our store we offer a ‘swap n go’ option. Cylinders are 2.6kg and on most tanks would expect a couple months, dependent on use.
  • A regulator and solenoid. A regulator controls the amount of co2 and pressure exiting the bottle. Usually it will have a gauge that shows the internal pressure and a gauge that will show the working pressure. A magnetic solenoid is used toter the flow of gas on or off, generally by use of a timer.
  • A form of diffuser/atomiser is required to diffuse the co2 into the water column. Thus, raising co2 levels your aquarium. Diffusers can come in two main forms, In-tank and In-line. In-tank is the most common way used to dissolve the co2. The diffuser is placed where it will receive flow. As a result, disperse the co2 through the aquarium. In-line diffusers are placed in the canister filter return hose. The co2 is diffused directly into the water returning from the filter, making it more efficient.

Note: Many inline diffusers and atomisers require 30psi minimum working pressure. Always ensure to check that your regulator is suitable.

  • Bubble Counter(can be inline or attached to regulator)
  • Co2 tubing.
  • Drop checker
  • Check valve

Co2 Kit Installation

  • 1) Attach regulator to co2 cylinder, ensuring seals are in place and not damaged.
  • 2) Open co2 cylinder tap to release carbon dioxide into regulator. The gauges should now show the working pressure and bottle pressure. Check for any leaks.
  • 3) Connect the bubble counter to the regulator.
  • 4) The co2 tubing can now be joined to the bubble counter and the other end connected to your diffuser of choice.
  • 5) Power on the Solenoid and check that the carbon dioxide is flowing into the aquarium through the diffuser.
  • 6) Always ensure there are no leaks at all joins. This can be checked with a little soapy water.

Setting the Amount of Carbon Dioxide in the Aquarium.

So all equipment is in place and you’re ready to set the amount of carbon dioxide going into the aquarium. There are a couple ways this can be achieved. Firstly it can be determined via the relationship between PH and KH. The optimum co2 levels in the aquarium with high light is 30ppm, although in lower light aquariums 15ppm would be sufficient.

Secondly, a drop checker can be used. Drop checkers work by constantly monitoring the PH of the water inside a vial containing bromothymol blue and 4KH water solution. The solution is relatable to the chart below in determining Co2 levels in the aquarium.

When diffused correctly into water, carbon dioxide will create carbonic acid. The carbonic acid will work against the buffering capacity of the KH(carbonate hardness) in the aquarium. Thus dropping the PH. Consequently, with some attentive checking of PH and KH it can be determined how much carbon dioxide is in the aquarium. As seen in the chart a PH of 6.6 at a KH of 4 you can assume the optimum co2 levels of approx 30ppm. Generally, a 0.2 drop in PH from prior co2 addition to post co2 addition is ideal.

Optimum co2 Levels

Setting the Amount of Time for Co2 Injection.

Plants will uptake most carbon dioxide at the start of the light cycle so it makes sense to be hitting the optimum levels at ‘lights on’. This can be done by timing the amount of time it takes for the co2 to drop the PH in your aquarium by 0.2. If it takes 1hr to do so, the diffusing should start 1 hour prior to the lights coming on. This can be achieved by a simple timer.

As plants will produce co2 and respire oxygen once lights turn off, the co2 needs to be turned off 1hr prior to lights out because this helps prevent oxygen starvation due to co2 levels being elevated.

For Information about Carbon and other deficiencies try this HELPFUL LINK

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