co2

Full Sized Pressurized CO2 Primer

A lot of people who want to start a planted tank have some kind of aquarium and fish keeping experience, but almost none with carbon dioxide (CO2). It’s actually counter intuitive to the old community fish tank, or to “reefers” who want to get into planted tanks. ”Wait, you mean I need to remove that cute bubble wall that helps my fish to breathe? So that I can put in a gas that can kill my fish?”
In this article I’m hoping to shed some light on what components can comprise a full sized pressurized system, and how they fit together.
Now I say “Full Sized” I am referring to a system using a tank with a CGA 320 fitting (To the best of my knowledge, a 5 lb tank is the smallest you can get with that). There are other ways to add supplemental Carbon Dioxide to your planted aquarium. These include Paintball systems (Red Sea makes one), proprietary systems (AGA for example), DIY (Do It Yourself) sugar and yeast mixture systems, and lastly CO2 by Electrolysis (Carbo-plus), however these are beyond the scope of this article although they might share some common components.
Components
Below is a list of components for a pressurized CO2 system. Not all are needed, but here they are:
  • CO2 tank
  • Washer
  • Regulator
  • Solenoid
  • pH controller
  • Manifold
  • Needle valve
  • Check valve
  • Bubble counter
  • Bubble counter liquid
  • Tubing
  • Inline reactor
  • Glass Diffuser
  • Venturi
  • Power Reactor
  • Bubble Ladder
  • Bell
  • Membrane Diffuser
  • Drop Checker
Description
OK, now for a brief explanation of what each part does, and how it fits into the system.
  • CO2 tank
CO2 Tank
5 lb. Steel tank with regulator
This is what makes the system pressurized. The tank holds liquid Carbon Dioxide, under pressure. They common sizes are 5, 10, 20, and 50 lb. That number refers to the weight of liquid stored in the tank, not the total weight (total weight will be the weight of the liquid plus the weight of the tank with CGA 320 valve). Tanks can be made of steel or aluminum. Aluminum being generally more expensive, but is also much lighter, not prone to rusting, and easier to transport. Now before you go buy one off eBay or some other online retailer, find out where you are going to get it filled. I get my 20 lb refilled at a place that does “swaps”. Some places will fill while you wait. On a “swap” you bring in an empty tank, and they give you a different full one. If you just paid for a nice, new, shiny, light aluminum tank on eBay, you just gave it to that company.
Another thing to consider is that these tanks have to be hydrostatically tested every 5 years to make sure they are not damaged, and can withstand the high pressure needed to keep the CO2 in its liquid form. If you bought one off eBay, you usually have to pay for that test the first time, and will after that. Another possibility is that if the tank fails the hydrostatic test, the tank is done, there is no fixing a failed tank, it’s now a paperweight. So if you are going to purchase a tank online, please ask for the date stamped on the tank.
Places to get them filled are gas suppliers, welding supply stores, beer distributors, and fire extinguisher stores. So before you buy, find out if where you will get your tank filled does swaps or will fill while you wait. CO2 tanks have a CGA 320 fitting to connect to your regulator (here in the US). One other thing I would like to mention is that you should secure your tank in some manner. This is especially true if you have pets, children, or can just have a clumsy episode. If the tank falls, and the valve breaks, you could potentially have a small gas powered rocket. I use bungee cords, either around stand supports or in conjunction with eye bolts.
  • Washer
Washer assemblies
Pictured from left to right Nylon, Fiber, Perma Seal MK I
This is a crucial little part of the system that can bring about a few headaches, so I thought I’d mention it. The washer is the component that makes a “air-tight” seal from the regulator to the tank. Usually I can get a few of the fiber ones for free when I get my CO2 tanks filled. There are a few different types that I’ve come across.
  • Fiber – Also known as a Cardboard washer. This is a disposable crush type washer. You use it once, and throw it away when you take thee regulator off. I’ve tried it once, but had a very difficult time removing it as it got embedded into the regulator.

  • Nylon – When I ordered my Milwaukee all in one, they gave me 2 of these Nylon washers. Shame I wish I could get more of these.

  • Perma-Seal – A reusable washer that is 2 bras discs with a compressable rubber ring. There are 2 Types: MK I which has a stem that needs to be screwed into a threaded fitting, and MK II which is just a flat washer.
NOTE: Applying Teflon tape or pipe dope to the threads on the CO2 tank will NOT seal it. In fact using Teflon on the threads is discouraged as any stray threads getting into your regulator can damage it.

  • Regulator
CO2 Regulator
Pictured: Regulator from Rex Grigg with Clippard solenoid, and needle valve
Liquid CO2 is under a lot of pressure to keep it in liquid form, about 1000 PSI (Pounds per Square Inch), which will vary with room temp. The regulator is a device that changes the gas pressure from one level (~ 1000 PSI in the tank) to a lower level (~10 - 40 PSI out of the regulator). Regulators can be purchased from about $60 up to and over $125, or you can assemble your own. In addition to some hand assembled regulators available, some of the more popular brands are Azoo, JBJ, and Milwaukee. Regulators should be able to attach to a CGA 320. I have a Milwaukee all in 1 on my 125 gallon tank. I did make some modifications to split the output, but on the whole am pleased with it, and its performance. In the beginning I had some problems obtaining a stable bubble count, but once I turned up the working pressure to about 35 PSI, and used the needle valve to fine tune instead of the low pressure knob (NOTE: the method I just described is opposite to what Milwaukee recommends in their instructions) that problem went away, and it should now help prevent an end of tank dump.

An end of tank dump is a very bad thing. A regulator needs a certain amount of pressure in the tank to work properly. When the pressure drops below a certain level, some regulators will “Dump” (release) the remaining CO2 in the tank. If not handled properly, this extra CO2 can end up in your tank with disastrous results.
  • Solenoid
Solenoid
Pictured: Clippard Solenoid & Clippard needle valve
This little electronic device, which is usually purchased with and is attached to the regulator acts as a gate to turn the CO2 on and off electrically. If you were to plug the solenoid into an outlet, you will have CO2 flowing 24/7. Another way is to have the solenoid plugged into a timer that will turn on the CO2 before lights on, and off before the lights. You can also plug the solenoid into a pH controller, for more control.
  • pH controller
Milwaukee SMS 122
Pictured: Milwaukee SMS 122
This is handy electronic device is used in conjunction with the solenoid. The solenoid is plugged into the pH controller, and the pH controller monitors the pH level in the aquarium via a pH probe. The pH probe goes into the aquarium, and tells the controller what the pH is. The controller checks if the aquarium pH is lower than a value set by you. If it is lower it turns off power to the solenoid shutting off CO2 flow. When the pH rises above the set level, the controller turns on power to the solenoid which turns on the CO2, and should drop the pH.
NOTE: pH probes need to be calibrated, and replaced every so often. If your probe is not calibrated, you can end up not injecting enough CO2 - or worse, injecting too much. The same can also happen if the KH (the measure of carbonate hardness) in your water supply changes, thus adding more buffer.
ALSO NOTE: In addition, please keep the probe wire away from your lighting wiring. I have experienced some pretty strange readings (in the 8 pH range, when it should be closer to 6.6) when my probe wire is in the vicinity of my lighting wiring, and the lights were on.
  • Manifold
CO2 Manifold
3 port manifold with 2 Clippard needle valves.
Manifolds are used to split the output of 1 CO2 regulator to 2 or more lines. I use one on my 125 to split the CO2 to 2 reactors on each end of my tank. If you want to run 2 tanks, or 2 diffusers, a manifold is needed. In my case the manifold is attached to the regulator, which has 2 needle valves each to their own bubble counters, each line into their own reactor. Some people would say “Why not just use a “T” to split the output?”. The reason is gasses will take the path of least resistance, and you will end up with 1 diffuser or reactor getting more CO2 than the other.
  • Needle valve
Needle Valves
Clippard Needle valve
Allows you to adjust the lower working pressure even lower into something that is more appropriate for an aquarium, and can be usually counted in BPM (Bubbles Per Minute) or BPS (Bubbles Per Second). Usually needle valves are used in conjunction with a bubble counter to see how much of a change you have made. There are also “Metering Valves” which are really an expensive type of needle valve. I picked up a Swagelok B-SS2-A metering valve from E-bay for less than $30 each. These allow much finer control than the stock, or a Clippard needle valve. NOTE: Some needle valves (like the Clippard) can be damaged if you try to use it to shut off the flow of CO2.
  • Check Valves
Check Valves
Plastic check valve, Clippard brass check valve
Check Valves stop water from flowing back up into the tubing if your CO2 is shut off or runs out. If water should get into the regulator, it can damage it, and/or drain your tank very slowly. Some people use the plastic airline versions. I did on my DIY yeast generator, but the plastic does become brittle over time, and will leak eventually compromising its purpose. Now I strictly use brass Clippard ones which are more durable.
  • Bubble counter
Bubble Counter
DIY bubble counters with Mineral oil
With some brands of regulator it comes built in (on). I have made some DIY ones from vials found at 'The Container Store.. They can also be made out of small water bottles. Basically a container is filled with a liquid, and a length of tube from the needle valve goes through the cap into the liquid allowing the gas to rise up through the liquid and into a second tube that is above the liquid line, and out through the cap to your distribution method. Now these are a good indicator for you when adjusting your needle valve. It lets you see how much of a change you made instantly without having to wait to see the effect in the aquarium water. On a DIY system this can act as a gas separator and keep any yeast gunk out of your aquarium.
  • Bubble counter liquid
The 3 most popular ones that I know of are: water, glycerin, and mineral oil. Whatever you use it should not react with the CO2.
Water: Most people can use water with no problems, but when I tried with my Milwaukee all in one, the level would drop over time. Turns out that under high pressure, the water would be minutely (so minutely that there wouldn’t be a water drop, or wet spot under it) pushed out thorough the bottom O-ring. A single wrap of Teflon tape on the bottom threads can fix that, but at the time I didn't know that and switched to...
Glycerin: A very thick viscous fluid which will make bubbles rise very slowly and easier to count. You might be able to find this at health and beauty aids stores, pharmacies or in Fleet Enema combined with “purified water”. However when I was running about 5-6 BPS the glycerin turned into a frothy meringue like substance. So I tried something thinner which was……
Mineral Oil: Thinner than glycerin, but thicker than water. This worked out very well for me. It can be found in most pharmacies, or in Ikea as wood cutting board treatment.
  • Tubing
Tubing
Pictured from left: Silicone tubing, Polyurethane tubing
Tubing side
Pictured from top: Silicone tubing, Polyurethane tubing
Provides a path to get your CO2 from the regulator to your distribution method. Some of the types of tubing that can be used are:
  • Regular (clear) vinyl airline tubing:
    Cheap, easy to purchase, however this gets brittle and cracks over time, resulting in leaks
  • Silicone airline tubing:
    Also cheap, easy to purchase, stays soft and flexible, but is slightly CO2 permeable (CO2 can escape through the tubing itself), resulting in a loss of about 6% per foot.

  • Polyurethane CO2 resistant tubing:
    (e.g. Clippard brand) is thicker walled, stronger, not as quite as flexible as silicone, but will last a long time without leaking CO2.
It’s not recommend to try and attach polyurethane tubing to anything glass including diffusers, and bubble counters since the walls are so thick, and rigid. One way around this is to run polyurethane tubing up to the edge of the tank, then put in the check valve, and then use silicone tubing to run underwater to your diffuser. Who cares if it leaks CO2 into the water column? That is what you are trying to do anyway.
  • Inline CO2 reactor
Aqua Medic 1000
AquaMedic 1000 CO2 reactor
The only commercial product I know that fits this description is the Aqua Medic 1000. I was using 2 of the AM 1000s to try and get the CO2 levels I wanted. It didn’t work, so I have since made my own. A DIY one is easy to make with some PVC (Polyvinyl chloride - tubing used in rigid pipe plumbing), PVC cement (PVC specific adhesive), and plastic or nylon hose barbs.
DIY Reactor
A DIY Reactor
Against conventional wisdom I currently have mine hooked up to my filter input. Basically water flows from the top of the reactor down, A CO2 bubble is released inside the reactor. The bubble trying to rise against the water flow will dissolve it. Some people place BioBalls in their reactor which will slow the water flow, and increase the bubbles contact time (if placed properly), and have a better chance of dissolving the CO2. However these supposedly can clog over time.
  • Glass Diffuser
Glass Diffusers
Pictured from left ADA pollen glass diffuser, unknown brand diffuser
Basically it's a fancy air stone similar to what you would put on an air pump. However they are more expensive, and make smaller bubbles which dissolve the CO2 much easier than a regular air stone. The trade-offs are that generally glass diffusers require more pressure to work than an air stone, and are much more expensive. Place this under you filter outflow so any bubbles that aren’t totally dissolved can be carried throughout the aquarium.
Maintenance Tip: Diffuser discs should never be scrubbed with a tooth brush or any other item, as doing so can damage the disc. Just soak in a 20:1 water: bleach solution, then rinse thoroughly, soak in an overdosed dechlorinating solution (something like Prime or Stress Coat), and I like to rinse thoroughly again.
  • Venturi

Venturi
A Venturi is essentially a section of pipe that has a narrow waist and an injection port at the narrow. As water flows through the pipe and the narrow waist it picks up speed, which creates suction at the injection port. The CO2 is broken up into Micro bubbles, and flow into the tank allowing a “CO2 Mist” effect. For the best results, Venturis should be placed where little or no head resistance as the back pressure will create larger bubbles. Venturis can add significant back pressure to the pump that is running it. Mazzei seems to be the gold standard with vanes on the interior of the waist aiding in the dissolving.
  • Power Reactor
Power reactor
There are manufactured and DIY ones. Basically it’s a power head attached to a tube that can hold a sponge at the opening. CO2 is injected into and chopped up by the power head impellor. The water, with CO2 bubbles, is forced down through the tube, and any large bubbles rise against the flow, other bubbles can be caught in the sponge (if present) until they dissolve. Generally this device is kept in the aquarium, although I’ve seen DIY versions that have the pump externally mounted on the aquarium.
  • Bubble Ladder
Nutrafin Bubble Ladder
Pictured: NutraFin bubble ladder
Imagine a maze for bubbles. Basically it’s a device that sits in the aquarium, and forces the CO2 bubble to travel a longer distance in the water column allowing more contact time, which will result in more dissolved CO2. Different variations of this can force the bubble to take a zigzag, or circular path. Once again, place this under you filter outflow so any bubbles that aren’t totally dissolved can be carried throughout the aquarium.
  • Bell
The CO2 bell is probably the simplest, albeit least effective method of dissolving CO2. It’s a container (a bell shape with a large mouth opening will be more effective) placed in high water flow area. CO2 is bubbled up and trapped in the “bell”. The water movement across the mouth will passively dissolve the CO2, and carry it through the tank.
  • Membrane Diffuser
membrane diffuser
This device operates similar to a bell in that CO2 is held in a high water flow area, and the CO2 is dissolved through the membrane (On one device I purchased it was 2 ceramic tubes). The description states 100% use of CO2, so you won't have to refill your supply tank as often. Unfortunately I found that in my tank with ~2 BPS in direct flow of my Eheim 2026 I was still getting a large (.75” - 1” diameter) bubble floating up every 2 minutes or so.
  • Drop Checker
Drop Checker
Pictured: ADA style drop checker
These are used to provide a visually indicator of the amount of CO2 dissolved in your aquarium. They can be made of glass or plastic, but it does require a transparent portion. You place water (reference solution) along with some drops of bromothymol blue into it. Don’t worry, it’s just your standard pH indicator solution found in most test kits. They can take some time (hours) to give you an accurate measurement of dissolved CO2.
  • How It Works
    A drop checker can work because CO2 goes into and comes out of solution relatively easily, and also likes to reach a point of equilibrium (where the amount in the liquid is at the same level as the amount outside the water). So the CO2 comes out of solution from the aquarium water in the airspace above the aquarium water, which in turn is absorbed into the reference solution & pH indicator reaching a point of Equilibrium. The addition of CO2 will lower the pH in the reference solution, and change the color shown. Yellow too much, green good, blue not enough.
    How to make it work better
    Using aquarium water as the reference solution works, and gives you an approximation of how much CO2 is dissolved in your aquarium. However by using a liquid with a known KH (usually 4 or 5 degrees), will give you a more accurate reading by negating any other buffering systems in your aquarium. Now, by using the color of the reference solution, and the pH/KH/CO2 chart (this can be found in many places on the internet),you can get a much more accurate, and reliable reading.
Carbon Dioxide in Planted Freshwater Aquaria


As with all forms of life on earth, carbon is the substance that is needed in the largest quantities. In fact, carbon accounts for about 43 percent of the dry weight of all plants. Plants have two different ways of finding carbon to use for growth. The first is from free carbon dioxide (CO2) captured from the water, substrate or directly from the atmosphere. In the absence of CO2, many plants have the ability to meet their carbon needs by splitting carbon directly from carbonates in the water, which is the second method.
While this second method is a useful adaptation in the wild, it is undesirable in the aquarium. When plants draw on the calcium carbonate in the water to meet their carbon needs (this process is sometimes called biogenic decalcification), the water has less and less buffering capacity, leading to serious pH fluctuations. Eventually, the plants can totally exhaust this carbon source as well.

There are several sources of CO2 within the aquarium. One fifth of the CO2 assimilated by the plants is actually returned to the water. The fish also add to the CO2 levels with their respiration. The bacterial decay of both dead plant material and driftwood decorations in the tank produce CO2. But the largest contributor to CO2 levels in the aquarium is the biofilter. In fact, a fully cycled biofilter will produce 1 gram of CO2 within 24 hours for every gram of dry food added to the tank.
In a properly stocked, moderately lit (no more than about 2 watts per gallon) tank with minimal aeration during the daylight hours, it is possible to have reasonably good growth without the addition of supplemental CO2. At higher light levels, CO2 supplementation becomes increasingly necessary. If measurements of the pH in the morning before the lights come on, and again in the late afternoon, are drastically different, it is a signal that the plants are using up all available CO2 in the tank. If the alkalinity (or carbonate hardness) of the tank drops over time, CO2 deprivation is almost a certainty.
The amount of CO2 needed in the aquarium for good plant growth is considered to be around 15 milligrams per liter (mg/L), although a range of between 10 to 40 mg/L is considered safe and effective. With good lighting, a moderately planted aquarium will consume 1 to 2 mg/L per during the photoperiod. Room air contains 1 to 3 mg/L of CO2, and aerated water dissolves only 0.7 the CO2 content of the air. From these figures it is easy to see why aeration should be kept to a minimum in the planted tank, and why CO2 supplementation is often necessary.
Without the plants that cover our earth, both terrestrial and aquatic, the atmosphere would not contain enough oxygen for us to breathe. We can use the oxygen-producing capabilities of plants to create a healthier environment for our fish.
Photosynthesis is at the very heart of the food chain. Plants (and certain bacteria) have the unique ability to directly harness the energy of the sun. This energy is used to convert water, CO2 and minerals in the environment into organic material in the form of plant growth. A by-product of this process is gaseous oxygen.

The process of photosynthesis is quite complex, and beyond the scope of this article. Those who are interested, (and it is a very interesting process) can consult any good encyclopedia. For our purposes, the important part to understand is that for optimal growth (and optimal oxygen production), plants must have a light source that is of sufficient intensity, correct spectrum and appropriate duration. They must have access to a continuous supply of CO2 during the hours that the tank is lit, and they must have a reliable supply of all the other nutrients they need.
Novice aquatic gardeners are often concerned that adding CO2 to their tanks will limit the amount of oxygen available for their fish. At the levels we are interested in maintaining in the aquarium, oxygen and CO2 coexist successfully. Adding small amounts of CO2 does not displace oxygen. In fact, the proper use of supplemental CO2 with appropriate lighting and trace element supplementation should actually increase the levels of dissolved oxygen in the water. Often, in a tank with really good plant growth, you will see bubbles rising off the plant leaves. This is oxygen being produced at such a rate that it can no longer be absorbed by the water. Its only course is to escape into the atmosphere.
At the temperature I typically maintain in my planted tanks, around 75 degrees Fahrenheit (24 degrees Celsius), the saturation level for oxygen is just over 8 mg/L (or 8 parts per million). For healthy fish and plants, it is recommended that oxygen levels not be allowed to drop below 60 percent of saturation, or in this case, about 5 mg/L. Below 2 mg/L, or 25 percent of saturation, your fish would be in serious trouble. (These figures are for freshwater only. Seawater has a lower saturation point.)
In my tanks, which are maintained at approximately 23 mg/L of CO2, the oxygen level hovers around 11 mg/L during daylight hours, well above 100 percent saturation. The buildup of oxygen during the daylight hours is such that even in early morning, before the lights are turned on, the oxygen has only dropped to about 8 mg/L. Oxygen bubbles start rising off the plants within an hour or two after the lights are turned on, as levels again climb above 100 percent saturation.
Properly monitored, supplemental CO2 will have no adverse affects on fish. CO2 is a gas that is easily driven off by surface agitation. In a tank with a heavier fish population, if the oxygen level drops below acceptable levels at night when the plants are not photosynthesizing, the operation of an airstone (on a timer set for when the lights are off) can easily drive off any excess CO2 and supplement the dissolved oxygen within the tank. In a properly buffered tank that is not overstocked, however, most people find that the oxygen level in the tank remains high enough, and the pH in the tank remains more stable, if the CO2 is left to run day and night without the interference of nighttime aeration.
Keeping the balance
Plants come from a number of different ecological niches. Some require extremely high light levels and correspondingly large amounts of CO2 and minerals. Many of our more difficult �bunch plants� are in this category. These plants are typically high oxygenators, as well.
Other plants have adapted to areas where the sun lovers can�t compete. These plants are generally slow growers, and do not give off large amounts of oxygen. Examples of these types of plants would be most Cryptocoryne and Anubias species. Many of these plants do well in relatively dimly lit tanks, and are not likely to exhaust the CO2 provided by the fish and biological activity in the aquarium. These plants show little, if any, direct improvement with light and CO2 increased beyond moderate levels.

A third group of plants, which contains the majority of popular aquarium favorites, is more adaptable. While they are capable of doing quite well without supplemental CO2 if given proper care, their growth is truly astounding in an environment of high light, additional CO2 and adequate trace element supplementation. Echinodorus and Hygrophila species come immediately to mind in this category, but there are many more.
It is important to remember that whether you use supplemental CO2 or not, the amount of light, CO2 and available minerals must be in equilibrium. If lighting is increased without adjusting the other factors, there is the possibility of biogenic decalcification. Excess CO2 is, at best, useless to the plants, and, as will be explained below, can be harmful to your fish. If the two major nutrients in the tank (nitrogen products and phosphate) are increased beyond the needs of the plants, you will experience algae problems. Many trace minerals, while absolutely essential to plant growth, are toxic in larger quantities.
CO2 and pH
There is a danger in using improperly monitored CO2. The presence of CO2 in water causes the pH to fall. This can be used to the aquarist�s advantage to lower the pH to the range preferred by most plants. However, if the water is not properly buffered, or if too much CO2 is introduced, the pH in the tank can drop quickly to levels that are lethal to fish. It is important to think of supplemental CO2 as an �additive,� just like fertilizers, pH adjustors, medications or even fish foods � all of which can create lethal conditions in your tank when added in excess. CO2 is no different. It must be used within specific parameters to ensure the safety of tank�s inhabitants.
CO2 produces a weak acid, and, as noted above, will lower the pH of a tank. For people with moderately hard water, this works out perfectly. Aquarists with water that has too much alkalinity may need to reduce the carbonate hardness (KH) by mixing their tap water with distilled or reverse osmosis water.

Those aquarists with very soft water must increase the alkalinity of their water. Without the buffering properties of KH, CO2 supplementation can cause the pH to plummet, to the detriment of plants and, more especially, the fish.
KH can be increased by the use of preparations sold exclusively for this purpose. For the more budget conscious, sodium bicarbonate (baking soda) or calcium carbonate can be added to tap water in small amounts to achieve a KH reading of between 3 and 6. Baking soda will raise only the KH. If both the KH and general hardness (GH) are too low, calcium carbonate is the better choice. One teaspoon of baking soda will increase the KH of 50 liters of water by approximately 40. Two teaspoons of calcium carbonate will increase both the KH and GH in the same amount of water by about 40. Another method of increasing both carbonate and general hardness is to prefilter water through crushed shell grit, crushed coral or dolomite gravel until the desired level is attained.
How much CO2 is enough?
As stated above, the recommended range for CO2 is between 10 and 40 mg/L. The goal should be to find a rate of CO2 supplementation that falls within this range, and produces a pH reading that is neutral (7.0) or slightly below. Avoid the extreme ends of this range. If your delivery system is not absolutely accurate, it is too easy for CO2 to move outside the recommended range.
There are commercial test kits available to tell you if CO2 is within the desired range. It is also possible to estimate the CO2 levels in your tank using the CO2 chart available at the Krib. You must know the pH of your tank water and the KH. Please be aware that this reading differs from total hardness, and buy a test kit that specifically measures the former.
Next month we will discuss the different options for providing supplemental CO2 in the planted tank.

DIY CO2

    Equipment Needed

  1. For this project, you will need a few household items and trinkets from the store. Depending on the size of your tank, you will need 2-liter soda bottles with caps to start. It is a good idea to have two bottles if your tank is 20 gallons or more. You will also need 100-percent silicone caulking, a drill and a bit slightly smaller than 3/8 inches. You do not want the anti-mold or mildew caulking.

    Purchase 3/8-inch silicone tubing from the pet store---not the clear vinyl tubing. Vinyl becomes brittle and will leak CO2. Also grab a check valve, which is important to keep the water from going backward should something go wrong. A T connector is needed to merge tubing from two soda bottles. The last piece of equipment, the glass diffuser, can be found online or through special order.
  2. Procedure

  3. Drill a hole slightly smaller than 3/8 inch into the soda bottle cap. Place the tubing about an inch into the bottle and caulk around the tube on the cap; connect the tubing with the T connector if using two bottles. Place the check valve between the diffuser and the bottles. Connect the other end of the tubing to the diffuser, and place the diffuser as deep into the aquarium as possible for maximum diffusion. Keep the soda bottles in an enclosed space, preferably below the tank. This is for aesthetic as well as practical purposes. If something gets blocked, the pressure of the CO2 will rise and the bottle may explode. This is why some aquarists opt against using a glass bottle in lieu of a plastic one.

    The recipe for the CO2 yeast mixture is as follows: 2 cups granulated sugar, water and ¼ tsp yeast. Some suggest warm water to activate the yeast; others say it does not matter. The same goes for the suggestion to stir the yeast in, as to help it dissolve. Once the sugar and yeast are in the bottle, fill it up to about 3 inches from the top of the soda bottle with water. A funnel is recommended for filling the soda bottle with the sugar. You'll know the system is working if miniature bubbles rise from the diffuser.
  4. Maintenance

  5. Every three to four weeks, check on your system to confirm the bubbles are still strong and present, that the tubing is clear of blocks and without leaks and to check the silicone caulking. About every month you will need to take the bottles out and replace the contents with a new yeast mix.