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The CO2 Fever: DIY CO2 Injectors

 Age of Aquariums > Aquarium Articles


Recently, with the help of the internet, and for being a very inexpensive and easy thing to make, the DIY (do-it-yourself) CO2 injector has become a true fever among aquarists. Some even say that its "a must for anyone wanting to keep live plants in the aquarium". As a result, there are lots of people out there using it without having the slightest idea how it really works, what its really for, and its relation to the other items in the setup. They just adopt the simplistic concept that "CO2 enhances plant growth", and start using it. Apparently its cool to say "I INJECT CO2", and everybody wants to learn how to make a DIY injector, even those who don't have live plants! This article will show how to prepare one (only a few lines are necessary for that) but, FIRST OF ALL, let's discuss the true necessity of CO2 injection and in which situations its an advantage.

After all, is CO2 really necessary?
The confusion begins in the question itself. If you want to know whether CO2 is necessary in order to have live plants in the aquarium, the answer is simple: YES! CO2 is a crucial item in the plants photosynthesis, a process where they take CO2 and, with the help of light and some other nutrients, transform it into sugars, carbohydrates and other vital compounds, releasing oxygen as a byproduct. Without CO2 the plants are incapable of performing their normal metabolism and quickly die. However, CO2 is a common part of our atmosphere (everybody knows about the "Greenhouse Effect", which results from the excess of CO2 in the air), and besides that it dissolves very easily into water. Hence every water always contains some concentration of CO2 dissolved in it. So the correct question is: "After all, is it necessary to inject EXTRA CO2 for the plants to grow in the aquarium"? And the answer to this question is also very simple: IT DEPENDS :-)

As we've mentioned, water always has some CO2 dissolved in it, which will be used by plants to perform photosynthesis. But depending on the other items of your setup, this quantity may or may not be enough for the plants to do it at a minimum necessary rate in order to stay healthy and beautiful. Some of these important items are:

  •  The levels of water temperature, pH and KH
  •  The amount and type of filtration
  •  The amount and type of plants
  •  The amount and type of lighting
  •  The amount and type of nutrients
  • Just looking at the list above shows that the subject is much more complex. Water chemistry is important because it directly determines the amount of dissolved CO2 that can stay in equilibrium with the CO2 gas in the air. Filtration and water circulation also affect the CO2 level directly, because just as it will easily dissolve in water, it can easily escape from the water. You can think of your tank as a big bottle of Coke, since the Coke´s "gas" is precisely CO2. What happens when you "shake" a bottle of Coke? The CO2 bubbles are released, right? The same happens with your aquarium...the more you "shake" the water because of filtration and circulation, the more CO2 escapes back into the air and thus the level goes down. The amount and type of plants also affects it because more plants means more CO2 consumption, and if the supply becomes short, they will have to compete for it. In this case the more adaptable and resistant species will survive at the expense of the more sensitive species. Lighting and Nutrients affect it because they too are part of the photosynthesis process. As we mentioned, theres a minimum rate of photosynthesis for them to grow healthy, but if you make a balanced raise of the LIGHTING/NUTRIENTS/CO2 trio, plants will happily accelerate their photosynthesis rate to abnormal levels and grow like crazy.

    Thus we arrive at the following conclusion: if you want to have an average quantity of healthy, good-looking, green-leaved plants, and your setup is such that lighting and nutrients are adequate and the level of dissolved CO2 is enough to guarantee the necessary photosynthesis, then the answer is: NO! You do not need nor should you inject extra CO2. Now, if you want a super-planted, super-lit tank with dozens of different species that grow super-fast, releasing oxygen bubbles at the end of the day, then we can say that it is indeed necessary to inject CO2.

    So what should I do then?
    Well, first of all NEVER, EVER believe that by simply injecting CO2 the leaves will stop going yellow or dying, and that the plants will start growing like crazy. This is completely wrong...CO2 does not solve the problem of withering plants! You'll only be putting the quality and stability of your aquarium at risk, and therefore the life of your plants and above all your fishes. If your plants are doing poorly, first you have correct all other items in your setup:

    • Provide adequate lighting. The subject of lighting for plants is also rather controversial and too complex to be discussed here. Look for other articles specifically about lighting;
    • Use some kind of gravel additive, and an adequately thick layer of gravel (the roots need to grow, in many species they are the ones responsible for absorbing most of the nutrients);
    • Also use a liquid fertilizer (in other species the nutrients are absorbed faster by the leaves);
    • Provide adequate filtration, not too strong and not too weak, never forgetting to do regular filter cleaning and partial water changes. Avoid aerators and filters that shake the water too much.
    • Preferably, keep pH between 6.2 and 7.4, hardness from average to low, and temperature between 20 and 27°C.

    Following this, most of the more common plants will probably be healthy and grow well, since photosynthesis will be functioning normally. don't be fooled by thinking that their growth is too slow. In nature, that is usually how it is. If and when all of this is working well, then you can start thinking about stimulating plants with extra CO2 (increasing photosynthesis), making them grow abnormally fast, releasing oxygen bubbles, etc. But in order to inject CO2, you should increase the other nutrients and lighting accordingly, or else you'll just be wasting CO2. It is often said that the lack of one of the three main elements to photosynthesis (nutrients, lighting, CO2), will limit plant growth. But this is also not completely true, since the excess of only one of these elements (or of a nutrient) may stop plant growth and/or favor algae growth.

    How to make the injector
    OK, if you've read and understood what'd been discussed above, then you're ready now to learn how to make and correctly use a DIY CO2 injector. which as we've mentioned is extremely simple.

    Material for the bottle:

    • 1 two-liter plastic bottle (with plastic bottle cap);
    • 1 thin plastic tube (the kind used in tanks with air pumps);
    • 1 airstone (optional);
    • Aquarium silicon sealant.

    Procedure: Make a hole in the bottle cap, such that the tube squeezes tightly through it. Insert the tube until its about 3 cm below the cap, and then spread silicon around the hole to seal it. Let it dry for a day. The plastic tube should be long enough to go from the bottle position down to the gravel in the tank. Put an airstone at the end of it if you want thinner bubbles.

    Material for the mixture:

  • 1 teaspoon of yeast;
  • 2 or 3 cups of sugar;
  • ˝ teaspoon of Baking Soda;
  • 1.5 liters of water (preferably filtered and free of chlorine).

    Procedure: Completely dissolve the yeast, sugar and baking soda into the water. Pour it into the bottle and seal it well. The production of bubbles will generally begin in an hour or so. A well made injector will keep producing bubbles for about 10-15 days.

    We have presented here only a basic description of how to set one up. There are many variants that can be found in articles around the net. There are also many comments and details that can help the user to improve or optimize the DIY injector, but this is also subject for other articles. The main reason for this one was to clarify and prepare anyone interested, so that he or she may make the decision based on objective information, not on fashion!

    Reader Comments Comentário

    Just a thought on this...I used a hotglue gun to attach my tube to the bottle and did it on both sides, and let the tube and cap cool in the fridge. Makes a wonderfully tight, inexpensive setup.

    Contributed by mmoyes

    Problems with the airtight seal? Get a connector valve, or better yet a check valve, or better than that, a check valve with a filter mesh. Drill a hole in the cap that will just fit the check valve and use plumbers glue to hold it in. The check valve and the bottle cap become one plastic. How to inject it? Use another check valve and some plumbers glue and drill a hole into the intake pipe for your canister filter. I've got the Lifeguard Customflo system and this method works perfect for the caps on top of the over the wall assembly. Careful, the flow of water perpendicular to the injection point pulls the CO2, if you don't use enough hose or add resistance it will collapse the 2 liter bottle.

    Contributed by Bently Durant
    Heinz bottle cap with pen Comentário

    I found a better solution than using a soda bottle. Heinz ketchup bottle comes with a hole in the cap already and all you need is to fit tightly the top of a roller pen that is a bit bigger than a hole. What I did is, I heated up a cone shaped metal just enough to melt a little bit the hole in the cup and squeezed in the pen top tightly (see photo). After that, all you have to do is to silicon a bit from both sides of the cap to prevent CO2 leakage (the idea is to put the pen part as tightly as possible and it works well). The only thing is that the bottle will smell for a while of ketchup. All you have to do is wash it up with hot water (NO DETERGENT) and put the empty bottle in a bag and then in to the freezer for a day. That should take the smell away. The rest is the way Marcos explained in his text.

    Contributed by Dusko Bojic

    If you're not good with your hands and don't want to fork out on expensive CO2 kits, you can invest in a Nutrafin natural plant system. It costs around £15 and is basically a manufactured version of the home made 'Coke bottle CO2 kit'. Aesthetically pleasing, reliable and easy to use. I have 2 in my 450 litre vision aquarium, and the plants are lush and growing well.

    Contributed by Jamie Ross

    I found using yeast for wine-making works better than bread yeast. It can live with high levels of alcohol, so it goes longer between changes. I use a 1 gallon pickle jar filled half full of distilled water. Then 1 cup of sugar, 1 cup of molasses an two heaping table spoons of wheat gluten. The molasses an gluten are harder for the yeast to break down an provide it with nutrents, usually lasts about 4 weeks.

    Contributed by Chad Highfield

    Here's another method for creating a large amount of CO2 whilst keeping to the correct levels during the dark periods. The way to ensure this is to run an airpump on a timer, to cause a large disturbance on the water surface at night, and the dissolved CO2 concentration in the water reduces considerably. When the air pump goes off in the morning the CO2 levels rise to their optimum. To create a large amount of CO2, a set of 4x2 litre bottles can be connected in series, with 2 of them containing a third of the standard yeast/sugar/water mix. The extra room in the bottles allows for equalized pressure and your valve to stay set, and adjustments only need to be made when the mix is starting to wein. As a rough guide, for every 10 litres of water, 1 CO2 bubble per minute is adequate.

    Contributed by Christopher Burton

    In addition to my aquaria, I am also a maker of home-made wines. A 20 litre carboy of fermenting THAT is a CO2 generator! But don't over-do it, a few hours a week of CO2 works well with my set-up. It takes some analysis to find out the optimum dosage based on tank volume, fish and plant populations, etc. Don't forget to install an anti-syphon check valve to prevent fishie stuff from ruining your prize winning Raspberry Blush.

    Contributed by Howard Ashdown

    Another way to attach the pipe to the bottle, and I think: the easiest way, is: drill a hole of 5 or 4,5 mm and cut the pipe in a way, that it has a sharp tip. By this tip, You can pull the pipe through the hole (You will need a combination pliers for doing this). It is tight, believe me! A friend always used glue and always had problems. With my method, he has no problems anymore!

    Contributed by Rich

    Great ideas everyone, however everybody seems to be missing an essential point. In order for the bubbles to dissolve better into the water, they must not be bubbles! You must put a diffuser on the end of the airline so that the CO2 particles are small enough to dissolve. If you don't diffuse the bubbles, they will rise directly to the surface and exit into the atmosphere.

    Contributed by Jack F

    I used the drill on the cap and pulled the tip of the hose through with a pliers. It fit really snug and was instantly air tight. I used a small air stone, about 2 cm and mixture as suggested. By next morning when the sunlight hit the tank, the air stone was already pushing CO2 like a mini water pump. More breathtaking was the amount of tiny trail of bubbles rising up from all the plants in the tank...this was amazing!

    Contributed by Shammy

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