CO2 Equipment for the Aquarium

by Tim Burton

So, you have read my articles on CO2, and have decided (or at least, thought about) using CO2 as the best method for you.  Terrific, where to start?


First, you will need to select a supplier of CO2.  More and more pet stores are carrying CO2 bottles; start by searching in your area for pet stores that offer this service.  If that proves fruitless, try specialty gas supplies, such as Praxair and Air Liquide, or you-brew beer stores, as these places use CO2 gas.


Once you have sourced your CO2, you will require a few pieces of hardware.  The first is a 2 stage regulator.  Basically, this equipment will reduce the pressure of gas that is flowing out of the tank (from about 600 psi) to a more manageable pressure of between 5-30 psi.  The regulator has two pressure gauges, the tank pressure and the working outlet pressure.  The tank pressure will show you when the tank is nearly empty; when the readings begin to fall, usually about 90%-95% of the useable CO2 has already been used up.  If you want to know the exact amount of CO2 you have before this point, a bathroom scale is the easiest.  Simply measure the bottle and subtract from it the Tare Weight-this is printed on the side of the bottle, it is the weight of the bottle empty.  The result is the mass of CO2 left in the bottle.  For example, if you weighed the bottle at 25 pounds, and the tare mass is 20 pounds, 25-20=5 lbs of CO2 remaining.  If you had a 10 lb tank, that means you have 50% remaining.


The next piece of equipment that is highly recommended is a solenoid valve.  This type of solenoid is open when plugged in, and normally closed.  While not essential, this valve will conserve much CO2 at night time by shutting off the flow of CO2 at night when a timer goes off.  Generally, have the CO2 solenoid open about an hour before lights on; this gives the CO2 time to build up to proper levels in the tank before the plants require it (I originally did not do this, and I had algae issues constantly.  Now, by making sure the CO2 is stable RIGHT when the lights come on has made a huge difference).


The solenoid can be alternately hooked up to a pH controller.  Please see this article for more discussion on this equipment.  As long as the hobbyists understand the limitations of a pH controller, I do recommend them.  The mistake most people make is they decide a specific pH is the target, and adjust the CO2 to that mark.  The proper method is to add CO2 while monitoring the plants and fish; once the correct level is determined, then maintain the pH at that level with CO2.  However, this method will also require that any buffers you add, such as bicarbonate, will need to be the same amount each water change (i.e. if you are aiming for a carbonate hardness of 4 degree, all water changes will need to be kept at 4 degrees as well, or the pH shift will make the pH settings of the CO2 controller meaningless). 


Many people, Tom Barr included, do not advocate the use of pH controllers because of the tendency of people to rely on the KH/pH/CO2 relationship table.  DO NOT USE THIS TABLE!  IT IS TOO MISLEADING!  If you are wondering what I’m talking about, I have purposefully not included this table on this website.  Check it out if you must on another site, but it is only an idealized set up relationships that is too easily thrown out of whack in an aquarium; please do not rely on it when setting up a target pH.  I do use pH controllers, but I use them only once I know what the right amount of CO2 in the tank is (and then measure the pH and keep it set to that amount).


The final piece of equipment, one that is arguably the most important, is the injector/diffuser.  There are more and more styles every year; some definitely work better than others.  The main division is if it operates by suction or pressure.  Pressure devices are similar to air stones.  They are usually ceramic diffusers that bubble a tiny stream of CO2 into the tank.  They are inexpensive, but usually a little inefficient.  They work well for smaller tanks, in general.  ADA, Red Sea, and Rhinox are all brands I have tried.    


Suction injections are more interesting.  These can be systems like Tom Barr’s venturi reactor (DIY CO2 Reactor) or Mazzei venturi injectors.  These operate under the principle of using a pump to create a vacuum that sucks in CO2 in such a way as to atomize the gas particles into very small bubbles (Micro Bubbles-an actual chemical term).  For mid-size and larger tanks, these are without a doubt the best system available.  I personally like the Mazzei injector I’m using on my own display tank.  However, I am currently unaware of a commercial source for these systems designed specifically for aquariums, but I’m certain they will be available soon for those not wishing to build their own.  If anyone reading this article knows of a manufacturer who is making a good suction driven system, email me and I’ll post the info.


Depending on your aquarium, you may opt for either system, either internal (inside the aquarium) or external (outside the aquarium).  There is no preference for their efficiency, this choice is mainly appearance and equipment.  If you do not mind seeing the injector in the tank, such as the beautiful ADA pollen beetle, then an internal injector would work for you.  If you would prefer to keep the equipment outside the tank, you have get in-line reactors as well.


This is all the equipment I use and recommend for CO2.  Designs for various installations are provided as links and images below.  The CO2 unit you decide to get is more a matter of what is available in your area (although the internet has many opportunities for sourcing CO2 aquarium supplies).  I will finish by saying that safety is the key when using compressed gasses.  Take precautions, such as securely fastening the CO2 bottle so it cannot fall over and empty its contents within 0.1 seconds inside your living room (this will not only scare the living daylights out of you, your cat, the neighbours 3 doors down, etc, but is a serious health risk, as people cannot breathe CO2, which is what all the O2 in the room will be displaced by).