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Understanding CO2 & Set-up Guide 



Understanding CO2 in Planted Aquariums

CO2 is arguably the most important element in the planted aquarium. It is required for respiration and growth by all aquatic plants, used in a process called photosynthesis. Plants require a constant supply of CO2 during the light hours, otherwise they can suffer. They combine the CO2 with water and light energy to produce oxygen and sugars to enable growth.

In the wild, plants get their CO2 in large quantities naturally from substrate (mud) and degrading plants. However, in a enclosed aquarium, CO2 is very limited. Water from your tap is depleted from CO2 and plant decay in an aquarium is minimal compared to the wild. This is why many aquarists have found out that supplementing CO2 really does help their plants grow much better and a lot stronger.

Deciding whether you need CO2 injection or not, or how much you need, depends on the amount of light you are supplying, and the selection of plants you wish to grow. However, for a more successful planted aquarium, we always recommend injecting CO2.

In low light aquariums, CO2 is not always necessary. Plants are less stimulated to grow under low light,  so extra injected CO2 is not required as there is normally enough CO2 supply coming from surface agitation, fish respiration and organic breakdown of dead plant matter. However, adding CO2 in a low light tank will still improve the quality of growth and health of your plants.

In aquariums with medium to high lighting, CO2 injection becomes vital. With more light available to the plants, the quicker they grow. This results in a higher demand for CO2 by the plants. Under medium to high lighting the aquarium becomes CO2 limited. The aquarist must now start adding CO2 to meet the plants demands. If the aquarium remains CO2 limited, your plants will suffer from growth deficiencies, and as a result you will experience algae formations.

What you need to get started with CO2 injection:

  • CO2 bottle - CO2 bottles come in various different sizes. The larger the bottle, the longer it's going to last you. A larger bottle also become more economical to fill up, saving you money in the long term. You will need a bottle with a standard UK fitting. All our regulators work perfectly with standard UK bottle fittings. They are readily available and probably best got hold of locally. We now stock CO2 bottles in 2 sizes and these can be purchased in store. Alternatively, we supply adaptors for sodastream bottles. This will allow you to use your CO2 kit with all sodastream cylinders, which can be re-filled by major retailers (Argos, Homebase, Tesco) for around £10-£12.
  • Regulator - Carbon Dioxide is introduced firstly through the use of a CO2 regulator. The regulator converts the pressure from the bottle to a lower, more useable pressure.  We stock a simple to use single gauge regulator which can also alter the rate of CO2 discharge via the needle valve that comes with it.
  • Solenoid - we love solenoids. They save you money and stop the wastage of CO2. During the "lights-off" hours your plants no longer need CO2, as they are not photosynthesizing. This therefore means we can turn the supply of CO2 off. This can be done manually by simply turning off the CO2 supply from the bottle. However, in an average household there is not always somebody around at the right time to do this. A solenoid valve and a timer will shut off the CO2 at the time you require. A wonderful piece of kit which comes with all our regulators. You will have to supply your own timer, any digital/electronic 24 hour timer will do, available from local DIY stores.
  • Bubble Counter - A bubble counter allows you to monitor the rate of CO2 entering your aquarium. It is an external piece of equipment that should be added in-line to your filter tubing. Whilst adjusting your regulator, you can use the bubble counter to count the bubbles entering your aquarium one by one. The easiest way to measure this is by counting the bubbles per second. Should you need to decrease the amount of CO2 in your aquarium, do so by reducing your bubbles per second.
  • Diffuser - a diffuser allows an effective method for CO2 to enter the aquarium. The CO2 is pushed through a porous medium that breaks down the gas into a fine mist of bubbles. These bubbles are then more easily absorbed by your aquarium water. Position your diffuser on the oposite side to your out-let flow. Your flow coming from your filter will then push the bubbles downwards, allowing for better diffusion rates.
  • Tubing - Tubing is needed to connect your regulator to your diffuser. The tubing needs to be safe for use with CO2. Regular air line tubing does not have the right properties so be sure to use CO2 resistant tubing. 

  • Drop Checker - The drop checker is another piece of kit used to measure the amount of CO2 diffused into your water. It is a little vessel that holds an special indicator liquid that changes colour depending on the concentration of CO2 in your aquarium water. Blue indicates too little CO2, yellow is too much, and green is the correct amount. Plants flourish best at around 30ppm underwater.  This is also a safe level for your fish. Too much CO2 and you put your fish at risk. Too little and there may not be enough CO2 for successful plant growth. Aim for green and alter the rate of CO2 using your needle valve and bubble counter.


Putting it all together:

Putting your CO2 equipment together is simple, once you know how! By following the diagram below you will have your CO2 system up and running in no time. 

Use a spanner to tighten the regulator to the CO2 bottle. Then attach all other compents together as displayed above. Once everything is connected together, open the needle valve slightly on your regulator before releasing the gas from the bottle. This will avoid damage to the solenoid when you first open the main valve on your bottle. Next, switch on the main valve on the bottle to release the CO2. The left gauge on the regulator should move to around 800-1000psi if the bottle is full.

To release the CO2 from your regulator, slowly turn the needle valve about half a turn and wait for the CO2 bubbles to be seen through your bubble counter. Using the needle valve again, aim for around 1-2 bubbles per second coming through your bubble counter (a higher rate may be required in larger aquariums). The needle valve is quite sensitive, so only small movements are needed to alter the rate of CO2. Over the next couple of hours monitor your CO2 levels using your drop checker. Adjust as necessary until your drop chcker fluid has changed to green. Remember, it takes around 1 hour for the drop checker to respond to levels of CO2. So when you look at your drop checker, it will be indicating the level as of 1 hour ago.

The solenoid can be set using a Electric plug timer to turn the CO2 off at night. Electric plug timers are available from any DIY store and most supermarkets. The solenoid valve will open when swicthed on, and close when switched off.


Top tips:

  • Turn your CO2 OFF 1 hours before the lights go out. There will be enough remaining CO2 in your aquarium for your plants during the last hour of your photo period. This will save you on CO2 consumption.
  • To start with, set the solenoid to turn ON the CO2 1-3 hours before lights come ON (may require a longer period in larger tanks). This will ensure the CO2 levels in your water are brought up to optimum concentration for the plants when the photo period starts. The most important time for your plants when they photosynthesize is at the beginning of the photo period. Aim for a nice green colour on your drop checker at the start of the photo period.
  • You may be required to do a little experimentation with your bubble count and CO2 on/off times. This is because every tank is different and will require differing rates of CO2 injection to achieve a green colour on your drop checker.
  • Be careful not to inject to much CO2 to high levels as this could harm your fish. Start low and work your way up to a optimum level for your fish and plants.
  • It is recommended to experiment with CO2 levels before introducing fish to the aquarium. This will avoid putting the fish at risk whilst you find the 'sweet spot' with your CO2 injection.