Author: Jay Hemdal
Everyone who has taken a sip of soda knows that gases can be dissolved in liquids. Aquarium keepers also know that their fish require proper amounts of oxygen dissolved in their aquarium’s water for the fish to survive. Advanced aquarists are also familiar with the uses for another gas, carbon dioxide (CO2), which is used as a nutrient for growing plants in freshwater aquariums and as a means to reduce the pH of seawater flowing through calcium reactors in reef tanks.
Carbon dioxide can have another effect on aquariums, though, resulting from the level of CO2in the air of the rooms housing them. The issue is simple: We know that elevated CO2in the atmosphere has been implicated in harming aquatic environments, particularly coral reefs and their ability to calcify. If we consider that buildings with good insulation exchange less internal air with the outside, causing CO2 levels inside to rise above normal levels, we can surmise that aquariums in such buildings exist in similarly CO2-elevated conditions as those causing deleterious effects on aquatic life. Read on to learn how using CO2in your aquarium can help you maintain a healthy habitat.
Carbon dioxide is a naturally occurring compound formed by the bonding of two oxygen atoms to one carbon atom. At normal temperature and pressure, it is a gas. In 2016, the average CO2concentration of the world’s atmosphere reached 400 parts per million (ppm), and it has been increasing over time. CO2dissolves in water, forming carbonic acid, which can lower the pH of the water.
Aquarium water can be easily tested for the presence of excess dissolved CO2using a good quality pH meter that has been recently calibrated with the three-point buffer method. First, get an accurate measurement of the pH of the aquarium itself. Then, remove a sample of the water (a quart/liter or so is fine) and aerate it very well for 24 hours. If the starting and ending pH levels are within .02 pH units of one another, the CO2level of the aquarium is in equilibrium with that of the air space that the aquarium is housed in.
If the pH rises more than .02 pH units, however, it indicates that there is surplus CO2dissolved in the aquarium water and that additional aeration of the fish tank is warranted. Theoretically, this aeration test could also result in a corresponding rise in pH over the 24-hour time frame. The only likely cause for the aquarium’s water being lower than equilibrium with the room air would be if the sample was taken at the end of the day, in a heavily planted aquarium.
Providing CO2for Aquarium Plants
Aquatic plants require light, nutrients, and carbon dioxide for photosynthesis. With the myriad of lighting products available today, the light requirement is easily met. Nutrients such as nitrogen and phosphorus are rarely lacking in aquariums housing fish (and if they are, they are easily supplemented). Carbon dioxide, then, is typically the factor that limits plant growth in freshwater aquariums. There are three basic ways to supplement CO2in planted tanks: constant supply, semi-automatic, and automatic.
The constant supply method generally utilizes a yeast reaction to produce a constant low-level stream of carbon dioxide for release into the aquarium. Some resourceful aquarists use the CO2produced by home brewing! The drawbacks to this method are the small amount of gas produced, that it is introduced to the aquarium continuously (even at night when it is not needed by the plants), and the need to frequently recharge the fermentation vessel.
The semi-automatic method utilizes a cylinder of CO2and a timer that actuates an automatic valve. During the day, when the aquarium lights are on and the plants are actively photosynthesizing, the valve opens, delivering CO2into the aquarium. At night, when plants are releasing carbon dioxide during reverse-phase photosynthesis, the valve is closed. This prevents wasted gas or potentially high levels of CO2at night. Be aware that the day/night cycle has a slight lag, so the CO2valve should be set to open about an hour after the lights come on and turn off about an hour before the lights do. The drawbacks to this method are the need for refilling the gas cylinders and the relative inflexibility of the manual gas flow setting, which does not take into account changing carbon needs in the aquarium as plants grow or are pruned back.
The fully automatic system also utilizes a CO2cylinder, but, in this case, rather than a timer, the automatic valve is actuated by a pH meter. As carbon dioxide is utilized, the pH rises. When it reaches a pre-set threshold, the valve opens, delivering carbon dioxide that in turn lowers the pH. When it reaches the low-side setting, the valve closes. This process delivers just the right amount of gas (assuming the pH range has been set appropriately). This method is the most efficient but does require careful monitoring of the pH calibration point; if the meter is reading incorrectly, the wrong amount of gas will be injected.
With all three methods, the carbon dioxide is introduced into the water through some type of diffuser that maximizes the rate that the gas goes into solution. Simply bubbling carbon dioxide into the water is wasteful, as most of the gas pops to the surface and escapes out into the room.
CO2in Reef Tanks
Carbon dioxide gas is used by some marine aquarists to better dissolve carbonate materials into the aquarium water, increasing the bio-availability of calcium, magnesium, and other elements for growing corals. The basic process is water from the aquarium flows past a needle valve that injects carbon dioxide gas. This lowers the pH of the water and increases the ability of the water to dissolve carbonate substrate inside a reaction tube. Inside the tube is a pH probe connected to a controller that opens and closes the valve to the CO2supply. This results in a feedback loop that maintains the pH of the water inside the reaction tube at a predetermined level. A good starting point is a pH pf 6.5, and this can be adjusted up or down depending on the specific conditions in the aquarium.
Calcium reactors are a good way to supplement marine aquariums with sufficient calcium to replace that taken up by actively growing corals. The choice of reactor media is important, though, as materials high in phosphorus will dissolve that mineral into the water at a high rate along with the calcium. Also, the pH meter used in the process must be calibrated frequently so that the pH set point remains accurate. And, as the media dissolves, it tends to pack in the chamber, so the aquarist may need to mix it up to allow for good water flow. Finally, if you are using CO2in an aquarium and the gas is injected at too high of a rate, free carbon dioxide can be released into the aquarium itself, with dire consequences. One way to reduce that possibility is to pass the effluent of the calcium reactor through a degassing chamber. For most home aquarists, a protein skimmer will serve that purpose well enough.
Calcium reactors have a very high initial equipment cost, as well as substantial ongoing operational costs that include replacing gas, media, pH probes, needle valves, and, possibly, solenoids.
CO2Dangers: The Mysterious Case of the Dying Boarfish Larva
I was involved with spawning and trying to rear the very delicate larvae of the boarfish (Capros aper) and had come up against a strange obstacle. The larvae needed to be raised in static containers of water—no aeration, as the bubbles would damage them. Once a day, I needed to count the remaining fish, which were very tiny, only 1/8inch (3 mm) in length.
As I put my nose close to the surface of the containers and began counting, some of the fish would begin to swirl to the surface and die right before my eyes. I jokingly told people that it was my ugly mug that frightened them to death, but, honestly, I was really puzzled… why would the fish die just when I looked at them?
In testing the CO2meter, I later discovered that watching the meter from a close distance would cause a dramatic rise in the meter’s readings—sometimes by as much as 500 ppm in just a minute or so. I now suspect that what happened with the boarfish was that my breath increased the CO2in a layer of air above the boarfish rearing tank, causing a pH drop in the container’s water that affected the larvae.
Testing for Surplus CO2
I have always thought that aquariums with photosynthetic organisms, whether corals, algae, or plants, would produce a surplus of oxygen during the day and then generate a surplus of carbon dioxide at night during reverse-phase photosynthesis. After all, that’s what happens in natural environments, such as ponds. One test puts some doubt into this idea.
I wrapped an established 5-gallon (19-liter) nano reef with a plastic garbage bag, set a CO2meter inside the bag next to the tank, and began taking readings. Since the tank lights had been on for a number of hours, I fully expected the CO2level in the air around the tank to soon begin dropping. Actually, the carbon dioxide level started at 875 ppm and climbed to 1020 ppm five hours later. Upon removing the plastic bag, the CO2level dropped to 815 ppm within 15 minutes.
It was obvious that this aquarium needed to vent a surplus of CO2, even during times of active photosynthesis. Does this same scenario carry over to other aquariums? Old rumors die hard, but the idea that the net carbon dioxide flux in aquariums equals out over a typical day/night cycle may not be true. It certainly wasn’t in this case.
I’ve used the CO2meter to test the air exchange rate in rooms holding aquariums. We had some low-pH issues in aquariums housed in a holding facility, and we wanted to determine if the issue was related to air exchange between the room and the outside through the HVAC system. We took an ambient CO2reading outdoors and then tested the air in the room. We discovered that the readings were comparable, so we ruled high carbon dioxide in the space as the cause of the depressed pH readings.
In another case, we discovered CO2 readings in a room that were greater than 800 ppm (although there were no issues related to this). Adjusting the outside air intake resolved that issue.
As an aside, the meter we have uses the “normal” atmospheric carbon dioxide level outdoors to calibrate the meter. The trouble is that this normal level was set by the factory at 375 ppm, which was a normal reading when the unit was constructed. However, today’s “new normal” of 400 ppm renders the meter inaccurate by a full 25 ppm!
In rare instances, the dissolved oxygen level of an aquarium may be at or near saturation, but artificially elevated carbon dioxide levels create symptoms in the fish that mirror those of an oxygen deficiency—rapid respiration followed by morbidity and death. There are two situations in which an aquarist is likely to see this problem: aquariums that have a carbon dioxide injector running at too high of a rate, or heavily stocked aquariums that have powerheads or canister filters whose effluents do not actively break the surface tension of the water. In the latter case, the high bioload adds carbon dioxide to the system and, because the surface tension of the water is not broken through aeration, CO2levels increase to unhealthy levels.
Knowledge Is Key
Carbon dioxide holds many benefits for both planted and reef systems, and advanced aquarists would do well to learn and apply the principles of dissolved CO2related to nutrient input in planted freshwater tanks and calcium dissolution in marine aquariums. But all aquarium hobbyists should have at least a basic knowledge of not only how to measure CO2 in an aquarium, and how the gas affects their tanks, whether it is purposefully introduced or already exists in the air around the aquarium.
The author is the Aquarium Curator at the Toledo Zoo and Aquarium (www.toledozoo.org/aquarium).
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For most of our tanks, lights and CO2 injection are turned on for a duration of 8 hours per day. For beginners afraid of algae, using a short light cycle such as 6 hours can be helpful. For stable, matured tanks, light duration can be pushed to 10hours+ without adverse effects.How many hours should I run CO2 in my aquarium? ›
For most of our tanks, lights and CO2 injection are turned on for a duration of 8 hours per day. For beginners afraid of algae, using a short light cycle such as 6 hours can be helpful. For stable, matured tanks, light duration can be pushed to 10hours+ without adverse effects.What is the best way to put CO2 in an aquarium? ›
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.How much CO2 should I use in my aquarium? ›
As a rule of thumb, for every 5 gallons of water, you should have 1 bubble per 3 seconds. So for example, for a 5 gallon tank, 1 bubble every 3 seconds. For a 20 gallon tank, 4 bubbles every 3 seconds.How much CO2 do I need for a 20 gallon tank? ›
However, for the average customer, we often suggest a 2.5–5 lb. cylinder for 20-gallon aquariums or smaller, a 5 lb. cylinder for 25- to 40-gallon aquariums, and a 10 lb. cylinder for 55-gallon aquariums or larger.Can too much CO2 hurt fish? ›
CO2 plays a vital role in the life of fish. Too much or too little will not only harm the fish but may lead to the untimely death. Fish produce carbon dioxide during respiration. Too much CO2 in the water increases toxicity and affects the pH balance.What are the signs of too much CO2 in an aquarium? ›
- Lowered Activity: Fish that are usually active hide or are less active, sluggish, signs of labored breathing, delayed reaction time in feeding.
- Position Change: Fish change their natural positions to favour positions closer to top of tank level or towards high flow areas.
CO2 Lowers pH
When dissolving CO2 into water (H2O), a small amount of carbonic acid (H2CO3) is formed. This mild acid has the effect of lowering the pH of your aquarium water.
And that is exactly why aquarium plants and algae are food competitors. When the plants grow well, there is hardly any food left for the algae and they wither away. CO2 fertilisation promotes the growth of the other plants and algae have no chance to grow!Does CO2 reduce algae in aquarium? ›
The good news is, YOU DO NOT have to experience algae in your planted aquarium. Algae normally appears when there is an imbalance in nutrients, CO2, oxygen and light. For example, too much light but too few nutrients and CO2 will cause algae. Poor distribution of CO2 and nutrients is also a common cause of algae.
Growth depends on how your aquaria are set up, especially with regard to lighting. If your lighting level is high, you are likely to have algae problems if you do not also add carbon dioxide; but with low to moderate lighting, added carbon dioxide is not necessary.How often do you add CO2 booster to aquarium? ›
Instructions. Add 1 ml. per 10 gallons of aquarium water. Dose once a day.How long does a 20lb tank of CO2 last? ›
This means the 20lb. tank should theoretically last 44 days (175/4), while the 5lb. tank will last about 11 days (44/4). These estimates do not take into account plant uptake of CO2, opening doors or curtains, or other opportunities for CO2 to escape and require replenishment.How long will a 10 lb CO2 tank last? ›
For example, if your homebrewing equipment features corny kegs (5-gallon capacity), a small 2½-pound CO2 tank will dispense for about 7 to 11 kegs while a 10-pound CO2 tank can last up to 44 kegs.How do I add CO2 to my cheap aquarium? ›
Aerosol CO2 sets are perhaps the cheapest and quickest way to add CO2 to a planted aquarium. They consist of a pressurised CO2 can, a hose, and a diffuser. Press the button on the can and the diffuser fills with Carbon dioxide gas.How many shots does a 20 oz CO2 tank shoot? ›
CO2 Paintball Tank! Refillable 20 ounce capacity tank BUILT FOR PAINTBALL. Featuring a lightweight, high-quality, durable, aluminum body for approximately 800-1000 shots per fill! This 20 oz.Does CO2 stress fish? ›
However, high levels can be detrimental because carbon dioxide reduces the ability of a fish's blood to transport oxygen. Fish in water with high carbon dioxide concentrations (>10 12 mg/L for some fish species) can suffocate even if oxygen levels are high.Will adding more fish increase CO2? ›
Fish produce CO2 as a byproduct of respiration - so the more fish in a tank, the higher the CO2 produced. Surface agitation increases gaseous exchange, the process of oxygen entering and carbon dioxide exiting the water. If there is not enough surface movement, CO2 remains in the water.How do I balance CO2 and oxygen in my aquarium? ›
Increasing water movement is the quickest way to increase oxygen (O2) levels in a fish tank, as it allows more O2 to dissolve and carbon dioxide (CO2) to be released. This can be easily done using an air pump, performing large water changes, manually stirring the water, or placing a fan near the aquarium.Should you run CO2 at night? ›
Growers can artificially increase the amount of atmospheric carbon dioxide (CO2) available to plants to improve growth and yield. But at night, plants do not uptake CO2 for photosynthesis. Maintaining artificially high levels of CO2 at night may, therefore, be wasteful.
Constant CO2 dosing
A more stable way of applying CO2 is to apply it below the normal levels and apply it so it is present in the water 24/7. This makes for a much more stable pH in the tank. CO2 is not enough to influence a huge swing, and the water stays slightly acidic as CO2 is constantly being pumped to it 24/7.
Carbon dioxide influences the pH of blood by reacting with water to form carbonic acid (H2CO3), which can dissociate to form a hydrogen ion (H+) and a hydrogen carbonate ion (HCO3-). Increasing the concentration of carbon dioxide in the blood therefore results in more H+ ions and a lower pH.How do I add CO2 to my aquarium naturally? ›
In fact, adding a few fish, shrimp, or snails is highly recommended because it will create a more natural ecosystem with higher CO2 generation. As previously mentioned, fish will exhale CO2, and the plants will turn these molecules into dissolved oxygen, thus creating a win-win situation for the tank.What are the pros and cons of CO2 aquariums? ›
Pros: Inexpensive to set up and run. Suitable for smaller aquariums. Cons: Uncontrollable and unstable CO2 levels. Unsuitable for larger aquariums.How much CO2 does algae need? ›
As trees and plants can capture CO2 for photosynthesis, so can algae which has an ability to capture and re-use up to 1.8 kg of CO2 per kilogram of algal biomass.Does algae thrive in CO2? ›
Algae are a group of aquatic organisms capable of photosynthesis. Seaweed, pond scum and giant kelp are some well-known examples. As a whole, algae have the potential to produce 10 to 100 times more fuel per acre of land compared to other crops, but requires lots of water and carbon dioxide (CO2) to grow.Will CO2 get rid of black algae? ›
Boosting the Carbon Dioxide levels in your aquarium can be an effective way to get rid of stubborn Black beard algae. Hobbyists must note that the process won't eliminate algae spontaneously, but it will highly inhibit its growth, thus eventually ceasing it to exist.Does algae need CO2 to survive? ›
Algae are typically photosynthetic, meaning they need carbon dioxide and sunlight to grow – just like plants.What causes excessive algae growth in aquariums? ›
Causes of Algae in Aquariums
Too much light or too many nutrients in the water will cause algae to grow rapidly. If you experience algae overgrowth, it could be caused by: Leaving house lights on too long. The tank receiving too much direct sunlight.
An aquarium air pump is a device that injects air into a tank's water. At the top of a tank, oxygen enters the water and carbon dioxide is released with the help of surface agitation.
Air stones replenish CO2 via surface agitation
Air stones help add CO2 to tanks that have been depleted of it. CO2 is crucial for healthy plant growth. It is absorbed into a plant's chlorophyll and converted into glucose and used as energy for plant growth.
Hydrostatic (Hydro) Testing is a process where components such gas cylinders are tested for strength and leaks. Aluminum CO2 cylinders require testing every 5 years. At the time of testing, a date stamp will be imprinted into the cylinder near the top of the tank.How much CO2 do I need for a 75 gallon tank? ›
Generally, I like 1-2 bubbles per second for most planted tanks under 75 gallons.How much does it cost to fill a 20lb tank with CO2? ›
Pricing for Refills:
20 Pound Cylinder: $39.89.
Refilling your CO2 canisters is much more cost effective than purchasing new ones each time. Depending on the size of your Soda Stream machine, you may be able to fill up multiple canisters for the same price as a single replacement.How many PSI is a 20lb CO2 tank? ›
A 20 lb. CO2 cylinder is filled with liquid CO2 by weight. At the time of fill the temperature of the charge is extremely cold and the pressure is around 100 psi.How many kegs can you get out of a 5lb CO2 tank? ›
How many kegs can I dispense with one CO2 tank? A typical 5lb. CO2 tank can dispense between 2 to 4 full-sized kegs, depending on the ambient temperature. The colder the ambient temperature the closer you will get to 4 kegs.How much does it cost to fill a 10 lb CO2 tank? ›
5 Pound Cylinder: $14.23. 10 Pound Cylinder: $28.34.How many psi is a full 5lb CO2 tank? ›
The pressure in a 5lb Co2 tank is on the order of 1200 PSI, and the average serving pressure is in the vicinity of 10lbs PSI. A regulator reduces the pressure to a more manageable level.What is the cheapest way to add CO2? ›
1. Slow-release CO2. This is by far the easiest and lowest cost method. You simply hang slow-release CO2 bags or bottles in your grow room.
Diffusers should always be placed in the down wash of the water outflow current; bubbles should be fine enough to get pulled by the current downwards when they first exit the diffuser.Can I use soda as CO2 in aquarium? ›
Soda water uses carbonic acid to produce CO2 so in theory it should work, but it is not that easy: carbonic acid is as the name says an acid, and any type of acid will lower the water's pH too fast for the fish and to some degree too fast for the plants to adapt to the changed pH.How many shots does 1 CO2 cartridge last? ›
HOW LONG DOES THE CO2 CARTRIDGE LAST? Once penetrated on the first trigger pull, the CO2 cartridge will last 24 hours or 21 shots.How long are CO2 cartridges good for? ›
All bottles should be replaced no later than every 24 months, even if you have not run out.How many shots do you get from a 12 gram CO2 cartridge? ›
One 12 gram CO2 cartridge can approximately deliver a minimum of 30 shots and a maximum of 200 shots if used from an air gun. However, a 12-gram CO2 cartridge can give you 20 to 30 good shots at once, and then you need to let it cool down before attempting the next shot.How long does 20 lbs of CO2 last? ›
This means the 20lb. tank should theoretically last 44 days (175/4), while the 5lb. tank will last about 11 days (44/4). These estimates do not take into account plant uptake of CO2, opening doors or curtains, or other opportunities for CO2 to escape and require replenishment.How long do you leave carbon in an aquarium? ›
Because activated carbon is so porous, it has plenty of room to both adsorb and absorb odor particles but will need to be changed every 3-6 weeks.How long does a 5 gallon CO2 tank last? ›
For example, if your homebrewing equipment features corny kegs (5-gallon capacity), a small 2½-pound CO2 tank will dispense for about 7 to 11 kegs while a 10-pound CO2 tank can last up to 44 kegs.Will adding CO2 reduce algae? ›
CO2 never directly prevents algae from growing? It helps the plants so the plants can prevent the algae from growing. It is an indirect contributor, but one thing makes carbon dioxide one of the best algaecides. One of the effects of carbon dioxide injection in the tank is it turns the tank water slightly acidic.Does adding CO2 increase humidity? ›
Co2 will increase the humidity of your grow, which in turn creates more moisture. More moisture you have in your grow means the potential for fungus and rot in your garden increases. Moreover, if you let your Co2 go unregulated it can create a toxic environment for your plants and yourself.
If you notice your plants get weak or yellowish at any moment, then stop using CO2 immediately and try to figure out what's going wrong. Either too much CO2 is accumulating or the temperature is not appropriate. CO2 should fall above the cannabis plants because it is a heavy gas that will tend to sink to the ground.How many gallons of CO2 in a 5lb tank? ›
A 20 lb. CO2 tank will yield approximately 90 gallons of soda, therefore a 10 lb. CO2 tank 45 gallons and a 5 lb. 22.5 gallons.How safe are CO2 tanks? ›
CO2 can be dangerous in a leak in a compressed CO2 system. Virtually every restaurant, bar or brewery in the country stores pressurized cylinders or tanks of carbon dioxide on premise. A CO2 leak inside an enclosed space, like the walk-in beer cooler, can become a potential death trap for anyone caught inside.Should I rinse carbon before putting in aquarium? ›
Don't forget to rinse any carbon filter before adding it to your aquarium. The small pieces rub together during transport, creating dust. You don't want black dust floating around your aquarium, do you? A quick rinse under tap water is all it takes to remove the majority of dust.Does carbon make aquarium water clear? ›
Carbon, or activated carbon, is used as a chemical filtration media. It helps to remove many organic and inorganic materials dissolved in tank water -- it keeps the aquarium water clear, and removes odors. Activated carbon works by using absorption and adsorption.Does activated carbon remove ammonia? ›
Activated carbon is an adsorbent that can absorb ammonia in the form of gas with a short contact time [10,11].