CO2 in your Planted Tank – FAQ’s Solved!


A planted aquarium with CO2 setup

  1. What purpose does CO2 (carbon dioxide) serve for a planted tank?

Carbon dioxide is the raw material that plants use during photosynthesis to convert light into food, fiber, and other forms of biomass.

  1. Will CO2 harm my fish?

CO2 will not harm the fish in your tank at normal levels (below 30ppm), but above this level is a different story altogether.

  1. What levels of CO2 should I have in my tank?

A majority of people with planted tanks maintain a stable CO2 level of 20 ppm, though this may be hard to do the do-it-yourself method. You will find a more extensive explanation is question #6.

  1. Are there different grades of CO2?

Yes. In the United States there are two basic grades of CO2. The first of these grades is the welding/food/beverage grade of 99.99% pure CO2, and the other is the Medical grade, which is 99.999% pure. The extra .9 costs significantly more, but you will find that there is very little difference, if any, between the two in terms of their efficacy.

  1. Is there any substitute for CO2?

Seachem makes a product called Excel, which is a source of organic carbon. While this product doesn’t offer all of the same benefits that natural CO2 does, it is a good carbon source for your plants.

  1. Will DIY CO2 work on my tank?

You will be able to make your own CO2 work in just about any tank. The only variable is how much work you are willing to put in to do this. It is extremely difficult to maintain stable CO2 levels if you are doing it yourself. A pressurized system is highly recommended for tanks that are over 25 gallons.

  1. What do I need for a pressurized system?

The minimal requirements for a pressurized system include a cylinder, regulator, needle valve, check valve, tubing, and diffusion method. If you wish to control the flow of CO2 with a timer or a PH monitor, you will also require a solenoid.

  1. What is a regulator?

A regulator is the device that converts CO2 in the cylinder to a lower, safer pressure so the plants in your tank can thrive.

  1. What is a needle valve?

A needle valve is a device that is responsible for lower the working pressure and controls the rate of flow in your aquarium.

  1. What is a diffusion method?

A diffusion method is what dissolved the CO2 in your tank’s water. There are numerous types of diffusion methods, but the main two are active and passive. Active diffusers combine the water and CO2 in a sort of current. Passive diffusers simply release CO2 into the water column so it dissolves on its own.

  1. What kind of tubing should I use?

You will be able to use whatever type of tubing you want, but I highly recommended that your steer clear of silicone tubing because it can lose up to 6% of CO2 per foot. Vinyl tubing is a good option but it can easily break down fast if it becomes exposed to sunlight. The right subbing in your aquarium can make a world of difference.

  1. Will the inexpensive plastic check valves work?

The cheaper plastic check valves will work but only for a little while. Since these valves tend to leak after a while, you should really consider investing in check valves that are made of some type of metal.

  1. What’s a solenoid?

A solenoid is an electrical valve that is typically closed, but it opens up when power is applied.

  1. Will the change in pH from the CO2 harm my fish?

CO2 does change the pH of the water, but your fish will not be harmed in any way. In the wild, changes in pH are typically caused by changes in kH or carbonate hardness, as well as TDS or Total Dissolved Solids in the water. These sudden changes can cause larger fish to experience osmotic shock. A vast majority of fish will be able to handle a more significant pH change because of hardness.

  1. Can I use my spare propane tank for CO2?

No, you definitely cannot. Propane tanks aren’t designed to hold the same pressures that CO2 cylinders are. Propane tanks are welded, whereas CO2 cylinders are completely seamless. CO2 tanks are specifically designed to hold pressures exceeding 1600 PSI. Propane tanks are built to hold 250 psi at most. The standard operating pressure for a CO2 cylinder at 70 degrees Fahrenheit is 800 psi.

  1. How do I know how much CO2 I have in my aquarium?

There are a number of different ways to measure the amount of CO2 in your tank. The first method is to use the pH/kH/CO2 chart, which you can find in my Guide. Keep in mind that there are some problems with this method, including that there can be small inaccuracies in your test kits, which can have negative implications for your tank. The other problem is that if any buffers others than bicarbonates and CO2 are being used in the water, your results will not be completely accurate. Peat, wood, and even some small rocks as well as pH buffers can throw off your results.

Another method that you can use to measure the level of CO2 in your aquarium is to take a water sample from the tank and simply measure the pH. Allow the sample you take to sit for 24-48 hours and measure it again. If you have a drop of even one degree in the pH, then you have 30 ppm of CO2. While it is true that this method works, it can be a bit slow and tedious. There is a new method that is becoming quite popular and it is called a drop checker. I won’t go into too much detail about this method, but you can check out the forums at www.plantedtank.com for more info.

  1. Is the electric method (like a Carbo-Plus) effective at making CO2?

The short answer to this question is no, not at all. You will find that these units cost just as much if not more than a pressurized system. In the long term it is much more costly to run these units than a pressurized system, and they also tend to strip the kH out of the water to make the CO2, which in turn has a negative effect on the water chemistry. With the electrical method you will have a very hard time maintaining healthy CO2 levels, which is why you will typically see these types of products on sale with a fairly huge discounted price.

  1. Will the pH drop/rise from CO2 hurt my fish?

No, it will not. The pH should drop once you have added the CO2 to your tank. If you are using a timer to turn off the CO2 at night, the pH will begin to rise. The changes in pH will not negatively affect any of the fish in your tank, so you won’t have to worry about that at all. This is because in the wild when pH levels rise or fall, there is always a change in the hardness and TDS or Total Dissolved Solids of the water. It is the change in the hardness and TDS, not the pH, that can cause Osmotic Shock among fish. Added or removing CO2 will not change the hardness or TDS, so there will be no effect on the fish.

Author: Tristan Gordon VIEW ALL AUTHORS POSTS

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