CO2 Basics and Diffusion Methods

Discussion in 'Planted Tank Equipment' started by Silikube, Jul 4, 2009.

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  1. Silikube

    Silikube Moderator Staff Member

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    In the Practical Fishkeeping Magazine, Issue 12 of December 2008, there is an excellently written article by the well known George Farmer. This is an online "adaption" of this article. I do not claim ownership and give full credit to Mr. Farmer for his wonderful work. I added some links and eye candy to this article, and with the help of Angus, we merged two very similiar threads to create this one. It serves as a useful source of info for those just getting started with injecting CO2 into your fishtanks.


    The most important nutrient for plant life is carbon "“ almost half their mass consisting of this element.Aquarium plants are no exception and carbon supplementation using carbon dioxide (CO2) injection or adding a liquid carbon additive boosts plant growth rates. With appropriate lighting and other nutrients, CO2 injection will boost growth up to ten times compared with non-CO2 enriched aquariums. With this increased growth, the plants will demand more of the other nutrients. CO2 injection is essential with higher lighting levels, so the plants are capable of utilizing all available light rather than allow algae to thrive.

    Gas injection also benefits aquariums with lower lighting levels, enabling success with a much larger variety of plant species. The ability to grow demanding plant species, such as growing a tight carpet of Glossostigma elatinoides will depend on good light, CO2 and other nutrient levels.The most popular techniques to introduce CO2 to the aquarium are the relatively inexpensive yeast-based systems, ideal for smaller tanks and for those on a budget "“ or pressurized systems superior in term of control, stability and reliability. Other methods include aerosols, tablets and devices that rely on electrolysis.Yeast-based systems rely on fermentation of yeast, sugar and water in a sealed container that produces CO2 then delivered to the water. Output tends to be unstable, so using multiple units and changing mixtures alternately can help produce a constant supply.

    Yeast based Example:

    DIY Fermented CO2
    Mainly used for smaller and low light tanks.
    This comprises of a sugar and yeast mixture in a soda bottle.
    Fermentation is affected by temperature and can be slow to start.
    The reaction will slow down when the yeast exhausts the available sugars of the newly formed alcohol kills the yeast.

    Advantages: Cheap,easy to setup.

    Disadvantages: Having to constantly monitor and recharge fermentor.
    Chances of yeast and sugar being pushed into your tank.

    This is a great cheap way to get into the hobby,but most people upgrade to pressurised CO2 after the bug has bitten.
    You can Google recipes and find which one suits you best.

    Note that the smaller bottle can be used as a bubble counter,and a yeast filter if the mixture expands out of your reactor bottle.

    Pressurised CO2

    Pressurized systems consist of a cylinder containing CO2 at a high pressure, a regulator to control the gas, bubble counter to measure gas rate and diffuser or reactor to introduce the gas to the water. Solenoids with or without pH controllers are optional extras that control gas supply as required.

    Pressurized CO2 Canister:

    If you use more than 2watts of light per gallon,or your tank is above 30 gallons.
    Unless you are growing Java fern and Crypts Pressurised CO2 becomes a must.
    This comprises of a CO2 cylinder,regulator,needle valve and a reactor.


    CO2 cylinder
    You can spend a fortune on a new branded cylinder,or you can modify a fire extinguisher.
    Cost R500-R2000
    There are quite a few brands available,but I definitely advise you to buy one that comes with with a solenoid and needle valve.
    It saves time and money.
    Cost R800 Ebay, R1650 LFS
    Needle valve:
    Hard to track down in SA.
    Ebay is best for this product.

    Advantages: Constant,controllable supply of CO2
    Disadvantages: Price

    Links to useful CO2 info sites:
    Getting Started With CO2
    Frequently Asked Q's
    Pressurized CO2
    Carbon Dioxide - CO2
    FAQs on Carbon Dioxide and Planted Tanks
    Setting up an Advanced Pressurized CO2 System
    CO2 & Water Hardness
    Do-it-yourself CO2
    DIY Yeast CO2
    DIY CO2 Recipe: Duration vs. Intensity
    DIY Yeast-Generated CO2 System
    Nyberg method for DIY Yeast
    DIY yeast mixture

    Diffusers and Reactors

    These allow the gas to dissolve into the water. There are various types, such as the ladder style diffuser that also acts as a bubble counter. Bubbles form at the bottom of the ladder and rise through the "˜steps’, reducing in size as gas dissolves.

    Ladder Diffuser:

    Other popular types are glass/ceramic diffusers that act as a fine air stone. Pressure builds behind a ceramic plate that has tiny holes, producing CO2 micro bubbles. These dissolve very efficiently, especially if there is good circulation, allowing better contact time between the micro bubbles and aquarium water. Glass/ceramic diffusers require regular cleaning, usually in bleach, to ensure maximum efficiency. A dirty algae-coated ceramic plate will produce larger bubbles that do not dissolve as well as tiny ones produced form a clean diffuser. Always soak the diffuser in a dechlorinator before re-installing into the aquarium.

    Glass Diffuser:


    In-line reactor:

    Theses are designed to fit in-line with an external canister filter output, The CO2 supply is fitted to the reactor and the gas/water mixture lows to the aquarium. These are almost maintenance free and hidden from view, but can reduce filter flow rate.
    Advantages: reduces equipment in the tank, less cleaning.
    Disadvantages: Expensive,but new cheaper models are on the market.

    Example and Theory Behind an In-line CO2 Reactor:


    DIY: You can put a tube into a power filter and you have a cheap effective diffuser.

    DIY Inline:I made this last year,copying a number of designs

    UP Aqua Atomizer

    [​IMG] [​IMG]

    "Designed to be installed outside of the aquarium, inline within the outflow tubing of your canister filter, either below the aquarium or mounted to the aquarium glass."

    Important things to know...

    "This professional quality diffuser requires a minimum of 36 psi working pressure. Must be used with CO2 pressure rated tubing only, not for use with silicone tubing. Tubing must be acid resistant and rated for high working pressure. Do not use with bubble counter fluid or other bubble counter oils. Fill bubble counter with water only to avoid contamination of diffuser."

    More useful Links regarding Reactors/Diffusers:

    DIY CO2 Reactor
    DIY CO2 Yeast Reactor
    How to Build a CO2 Reactor
    Tiny Super Efficient CO2 Reactor
    DIY Inline-reactor Plans

    Bubble Counters:
    These little gadgets are visual indications of your CO2 flow rate. This is done by counting the bubbles entering the little device from your CO2 system, often reffered to as "bubbles per second" (b.p.s.) in planted aquaria.

    Store Bought Bubble Counter:

    Example of a DIY Bubble Counter:

    pH Controllers:A few brands are available ranging from R2000-R6000
    These allow you to set a pH and the controller will turn off the CO2 when you achieve it

    Water chemistry

    CO2 is toxic to fish and inverts with levels exceeding 30-35mg/l (ppm). With low oxygen levels this figure is reduced, which is why a fair amount of surface agitation could be helpful. This will drive off CO2 as it is very unstable in water, so gas consumption will increase. This is a trade-off worth considering. When CO2 dissolves in water, it creates carbonic acid that reduces pH. This can be beneficial for two reasons. Firstly, most freshwater tropical fish prefer pH neutral and slightly acidic water (pH 6to7) that will be produced by CO2 injection in most aquariums. Secondly, the ammonia and ammonium balance is shifted to less toxic ammonium as the water becomes more acidic. Increased plant growth leads to more oxygen production "“ in other words increased photosynthesis. Many planted tanks experience this oxygen as bubbles know as "˜pearling’.


    CO2 Testing

    CO2 can be measured by testing the aquarium pH and KH (carbonate hardness) levels with test kits. The results are then cross-referred to a pH/KH/CO2 chart found on the internet. However, this method is not very accurate as it relies on carbonic acid being the only influence on the tank water’s pH. There are other acids, especially in mature aquariums, such as nitric and humic, so the CO2 reading may not be accurate.

    German pH/KH/CO2 chart:
    (Although in German I think it's pretty self explanatory)

    Another popular test technique is with a CO2 drop checker. This permanently sits inside the aquarium and gives an instant indication of gas content. It is filled with a mix of exactly KH 4 water and pH reagent and the solution will be blue with too little CO2, and green with 30ppm and yellow with over 30ppm CO2. One of the biggest causes of algae in a well-planted tank is fluctuating gas levels, so providing a stable level during aquarium lighting is essential.

    Example of a "CO2 Drop Checker":

    How To Use A Drop Checker
    The Three-way KH-pH-CO2 Relationship
    Measuring CO2 levels in a Planted Tank


    For those not wishing to add CO2, but want to improve plant growth, there are liquid carbon supplements. Easy Life Easycarbo and Seachem Flourish Excel both contain an active ingredient that supplies carbon with a side effect of being a mild algaecide. Dosed daily, they will significantly improve plant growth and combat algae. In a smaller tank running costs are relatively low, with a 500ml bottle lasting 12 months in a typical 25l tank. These products will not stimulate as much growth as CO2 injection, so is beneficial for those who wish to still grow demanding plants with out the fast growth and maintenance CO2 injection provides. Some 100% aquatic plants like Vallisneria, are sensitive to these products, especially if overdosed.

    Flourish Excel:
    [​IMG] ... Excel.html

    Cost: +-R180 per 500ml bottle

    Easy Life Easycarbo:
    Last edited by a moderator: Apr 11, 2014
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  2. R.C.

    R.C. Moderator Staff Member

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