CO2 injection

Plant tissue analysis revealed how important Carbon was when almost half of plant mass was Carbon. Since the discovery greenhouses started releasing free CO2 gas inside closed growing operations in order to increase production. Planted aquarium hobbyists looked at possible CO2 addition (1962) also, but only recently few years ago this idea became popular with high tech systems. The reason why it took so long was the development of good fertilizers to support CO2 injected high growth rates for one and also the complexity of such systems to deliver and regulate it. At the same time locally available plants grew just fine under relatively low lights.

FAQ

Should I use a CO2 Controller?

CO2 controllers do more harm than good unless used with hard water and high KH. They don’t regulate CO2, instead they are chasing after pH dependent on KH levels. When KH fluctuate then CO2 is a mess.

How plants grow without CO2 in low light setups?

Some plants can get Carbon from other sources like carbonates –CO3 known as KH, carbonate hardness comes from tap and some substrates. This is why some aquariums lose KH.

Low light setups don’t need CO2?

It depends on plant specie. Some need Carbon from CO2 even under low light, others can uptake carbonates instead but still prefer CO2 if available. So supplying low levels of CO2 will increase plant health under any light intensity.

How does the CO2 get in the water?

CO2 gets in the water several different ways. From the air: There is CO2 in the air we inhale and lots in the air we exhale out, many other sources as well, industrial and road traffic. From the fish: Fish inhale Oxygen and exhale CO2, just like a humans. Since the fish are breathing in water the CO2 is released into the water. This however supplies only little CO2, about 0.6ppm which keeps some plants barely alive. To get more CO2 we need CO2 reactors.

How much CO2 do I need in the water?

A good target to start is 1 bps (bubble per second) for medium size aquariums which is simple to do and safe to fish and sufficient to plants. Maintaining 10 ppm under low light will increase plant health significantly. Maintaining about 20 ppm under medium and high light is more desirable to provide sufficient Carbon for the plants. Exceeding levels of 30 ppm doesn’t allow much of a safety margin.

Do I need to shut off my CO2 at night?

No. CO2 is available in the water full-time in nature, no reason to change that here. Since we are dosing at a lower level (20 ppm) we have plenty of safety margin. And stable pH and CO2 levels help plants and fish, making it harder on algae.

Do I need to test for CO2 levels?

It is a good idea when starting up a new aquarium to learn what is actually happening and how things work. When system breaks in there is little reason to test often. Why? Because if the CO2 gas is supplied continuously and dissolves in the water and there is little surface agitation then it can not disappear.

How to test for CO2 levels?

There are few methods. The easiest is to test for pH and dKH and read the value from CO2 Table, see bellow. Click on image to open to read or print.

Another method is to download an Excel Spreadsheet for PPS and type pH and dKH and read the CO2 levels calculated automatically. Both methods are pretty accurate unless there is something in the aquarium altering pH, like some organic substrates do, pH buffers or humic acids. In such case a drop checker can help.

How Carbon deficient plants look like?

Plants grow slow and short with small size leaves developing holes.

What happens when CO2 overdose?

Plants don’t mind but fish do. Fish look stressed, swim upside down, and lose sense of direction and some try jump out of water. If conditions don’t change fast enough, fish slow down to narcotic sleep and death. To help CO2 poisoned fish install air stones and pump as much air as possible, make surface agitation with HOB filters and power heads.

Is air stone and HOB filter ok with CO2 injection?

Yes, slow aeration is necessary by either HOB filter or air stone set to minimum flow.

How can I control injected CO2 quantity?

CO2 flow and quantity can be approximately adjusted and monitored with a Flow meter RMA-151-SSV 5-50 cc/min.

How old is CO2 injection idea for aquatic plants?

The oldest is a TFH article printed 1962, see bellow.