Do I need to inject CO2? How much do I need to inject?

The fundamental thing is that all plants NEED a source of carbon. No ifs and buts. How they get it is another issue, they can get it from CO2, from carbonates and the likes but CO2 is the easiest source for them.

Plants need a sufficient and stable source of CO2 that is well circulated.

The question becomes now, do I need to inject CO2?

The answer is in the form of another question, which is, how much lights do you have?

Plants are reactive and how much nutrients and carbon that they need will depend on how much light they are exposed to.

If you have a lot of lights shooting onto the plants, naturally they will react accordingly and request for more nutrients and carbon from their surroundings. If you do not have high lights, then naturally the rate of growth of the plants will slow down and they will require less of carbon and nutrients.

Its like humans, if you exercise or engage in activities of high cardiovascular activities, naturally you need more food and water. Drinks like Gatorade replenish what we lose when we exercise and we build muscles in the process. It’s a far-fetched analogy but I think it works in this case.

Normal water in a glass cup or in the aquariums has around 3ppm of CO2. That’s about the natural composition of the air in the water. It can be a little more or a little less, depending on where you situated and other miscellaneous factors.

Now that we are clear of the basics, the next question to ask is, how do we measure how much lights we are shooting into the tanks?

One easy and widely accepted method is to calculate the Watts Per Gallon (WPG). This is taking the actual wattage of your light tubes and dividing it by the amount of water you have in the tank in gallons.

The general breakdown is this:

• Less than 1.5wpg, no need for CO2 injection.
• Between 1.5wpg and 2.5wpg, depending on the situation
• 2.5wpg and above, there is a need for CO2 injection

The area between 1.5wpg and 2.5wpg is a grey area because it depends on how much plants you have and how well the circulation is. There is no fixed rule. People having 2wpg usually don’t have much issue without CO2 injection but they made sure that they have good surface agitation (to promote healthy gaseous exchange) and excellent circulation.

The WPG rule is more suitable for FL and PL light fixtures. For T5 HO and MH light fixtures, they don’t follow this rule. Usually when you shooting T5HO and MH lights, chances are you will need CO2 injection as these lights are of much higher intensities. Anything with 2WPG for these light fixtures will warrant CO2 injection.

Next, how much CO2 do we need?

There is never ever a rule on a tank of this size needs how many BPS (bubbles per second). A 2 footer tank will never require 2 BPS and a 3 footer never needs 4BPS.

This is because every tank is different. A 2 footer with 60watts of light and a 2 footer with 45 watts of light, will they need the same amount of CO2? How about a tank with a lot of plants and a tank with just a few bunches? And how about a tank that uses a reactor while another uses a diffuser?

This answer to all of the above is NO. They will have differing needs, a tank with more plants naturally needs more CO2 than the tank of the same size but with less plants.

The most important point is thus the more ambiguous one. You have to go through several rounds of adjustments before you can get the correct range for your individual tank.

The key is that you can start a little lower, for example, a safe number to start with is using half the size of your tank. For example, a 2 footer should start with 1 bps first. A 3 footer probably around 1.5bps.

The reason for this is that fishes need time to acclimatize to the change in water parameters. You can increase the CO2 by about 0.5bps daily as to ensure that your fishes are healthy.

There are 3 ways of determining how much CO2 your tank needs.

1st way is simply by trial and error. You will adjust the BPS until you see that your fishes exhibit signs of stress and you adjust it back down by 0.5BPS. An example would be when you increase the BPS to 3 and realize your fishes start to gasp, you would adjust it back at 2.5BPS.

This is straightforward but risky. Only for the experts.

2nd way is to use the pH/KH to determine the exact ppm of CO2. Plants enjoy excellent growth with a level of 30ppm or so. This can only be used if you do not have any pH or KH altering medium/substrate. If you use ADA Aquasoil, peat , coral chips or other similar items, then it cannot be used.

3rd way is to use a drop checker. However, do not use the tank water. Instead, use a KH4 solution to ensure that you are getting the correct results. To use it, put the liquid provided with the drop checker together with a KH4 solution. Place it away from the CO2 injection location (i.e., away from the diffusor). To get a KH4 solution, you can either buy it online (just google KH4 solution), or you can create your own (slightly inaccurate) solution.

To create the KH4 solution, you will need:

• Distilled water (Watson’s Distilled water, for example)
• Baking Soda
• KH Test Kit.

To mix, add in the baking soda bit by bit and measure the KH at intervals. Stop when you get a KH reading of 4.

Now, when you have your method of measurement and determine the correct injection amount, take note that you have to increase it over time as the tank matures. This is a simple logical thought because as the tank matures and the plants grow in numbers and mass, they will need more carbon. 3 people will need more food than just 1 person.

Next, what should you watch out for when you inject your CO2?

There are many ways to inject CO2 and all have their pros and cons. The more important aspect is to ensure that it is well circulated and is stable.

Ensure that there are no dead spots by playing around with the filtration output. If you are using a rainbar, try a few different positions and see which gives the best result. You can test it by dosing some dry ferts or just some small sinking food. If most of them just flow straight down, then you know you have to change the return direction/rate.

Secondly, you need to have a stable source of CO2. For the entire photoperiod, you have to have a stable CO2 levels as plants are not as quick to adapt to the swinging levels.

To do this, switch on your CO2 prior to your photoperiod. The time needed would depend how your circulation/injection method/BPS but anytime around 15-20 minutes should be sufficient. Any longer than 30 minutes mean that something is wrong.

In a nutshell, CO2 is one of the most important variables in ensuring that our plants are healthy.

The basics are that the CO2 has to be sufficient, stable and well-circulated. Whether to inject CO2 or not would depend on how much lights you have. To determine how much CO2 you need to inject, you have to adjust accordingly as every tank is different.

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This is a total rewrite of what I did previously, prior to the server crash that made me lose the earlier post on this.

I will try to update more things in the future, like the various methods of CO2 injection or carbon introduction.

This is not definitive and alot of people will surely beg to differ as to what I have written, but most of this comes from what I have done, seen and heard so it should be reasonably accurate, though I take no responsibilities for any loss of fauna, flora or other mishappenings.

I hope this thread will allow more people to have a better understanding of our plants and no repeatedly asking the same questions.

If you have anything to share (or differ, which is perfectly fine) I will compile the postings and tidy them up over here.

Contributions will be duly noted.

[EvolutionZ]

just to add on.
WPG rule DO NOT apply to small tank.
from the smallest tank to 2 - 2.5ft are considered small tank.

it also doesn't work for very big tank

Originally Posted by Shad0w

it also doesn't work for very big tank

it does but u need more CO2 pumps

[m2cys]

Very useful info... thanks!

what if my WPG is only 0.3? i'm using a 3ft light on a 4ft tank