Rex's Planted Tank Guide

CO2 For The Planted Tank – Frequently Asked Q's

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1. What is CO2(carbon dioxide) to the planted aquarium?
Carbon dioxide is the basic raw material that plants use in photosynthesis to convert light into food, fiber, and other forms of biomass.
2. Will CO2 harm my fish?
Short answer: NO. Long answer: At the levels we normally try and maintain in a planted Aquarium (~30 ppm) the CO2 will not harm your fish.
3. What levels of CO2 should I have?
Most people try to maintain a CO2 level of 30 ppm however this may prove to be difficult to do with the d.i.y method. Explain further in question #6
4. Are there different grades of CO2?
Yes, in the United States there are two basic grades of CO2 that you can find. Beverage/food/welding grade which is 99.99% pure CO2 with the main contaminant being water. The other grade is Medical grade. Medical grade CO2 is 99.999% pure. That extra 9 costs a lot of money. Some places will try and tell you that there is a difference between welding grade and food/beverage grade. If this is the case then that difference happens at their location. If you could be there when the CO2 truck comes you would find that they fill both containers from the same truck.
5. Is there any substitute for CO2
Seachem makes a product called Excel that is a source of organic carbon. While it doesn't have all the benefits of CO2 it does provide a carbon source to your plants.
6. Will DIY CO2 work on my tank?
. You can make DIY CO2 work on most any tank. The question is how much work are you willing to do? Also it's very hard to maintain stable CO2 levels with DIY systems. For any tank over 25 gallons I highly recommend a pressurized system.
7. What do I need for a pressurized system?
The minimum needed for a pressurized system is: Cylinder, regulator, needle valve, check valve, tubing, diffusion method. If you want to control the flow of the CO2 with either a timer or a pH monitor then you also need a solenoid.
8. What is a regulator?
A regulator is a device that converts the high pressure CO2 in the cylinder to a lower safer working pressure.
9. What is a needle valve?
A needle valve is a device that takes the working pressure to an even lower pressure and controls the rate of flow into your aquarium.
10. What is a diffusion method?
A diffusion method is what you use to actually dissolve the CO2 into your water. Their are many different types. But they break down into two major types. Active and passive. Active diffusers mix the water and CO2 together in some sort of current. Passive diffusers just release the CO2 into the water column to pretty much dissolve on it's own.
11. What kind of tubing should I use?
. You can use what ever tubing you have on hand. But you should try and avoid silicone tubing as it can lose up to 6% of your CO2 per foot. Vinyl will work but if exposed to sunlight it can break down pretty quickly. Having the right tubing can make a huge difference.
12. Will the inexpensive plastic check valves work?
For a while they will. They tend to break down and not function or even leak after a while. The best check valves are going to be some sort of metal check valve.
13. What's a solenoid??
A solenoid is a electric valve. For aquarium use we use “normally closed” valves. When power is applied to these valves they open up.
14. Since CO2 will cause the pH to go down will this change in pH hurt my fish?
No. Normally in the wild pH changes are caused by changes in the kH (carbonate hardness) and TDS (Total Dissolved Solids) in the water. These changes can cause osmotic shock to the fish if they are large enough. Most all fish can handle a bigger pH change due to hardness than many people think. In many places where our fish come from a rainstorm can cause a huge change in pH. When CO2 lowers the pH it doesn't affect the kH or TDS. So the osmotic balance is not upset.
15. Can I use my spare propane tank for CO2?
No. Propane tanks are not made to hold the same pressures that CO2 cylinders are. Propane tanks are welded tanks. CO2 cylinders are seamless tanks. CO2 tanks are built to hold pressures over 1600 PSI. Propane tanks are built to hold at a maximum of 250 psi. The normal operating pressure for a CO2 cylinder at 70°F is 800 psi.
16. How do I know how much CO2 I have in my aquarium?
.There are several ways to measure your CO2 levels in your aquarium. One is using the pH/kH/CO2 chart. You can find one in my Guide. There are some problems with this method though. One is that small inaccuracies in your test kits or your use of the test kits can lead to big mistakes in how much CO2 you think you have in the tank. The other major problem is that if there are any buffers besides bicarbonates and CO2 in the water you will not get accurate results. Peat, wood, some rocks and pH buffers can skew the results. Another method is the pH drop method. Take a water sample from your tank and measure the pH. Now let the sample sit for 24-48 hours. Measure the pH again. If you have a 1° drop in the pH then you have 30 ppm of CO2. It works but it's kind of slow. A new method that is gaining popularity is a drop checker. I'm not going to go into detail about that method here (if someone wants to write it up I will include it here and in my Guide). So head over to www.plantedtank.net and check the forums there. One thing to note, if you are NOT injecting CO2 then you only have 2-3 ppm no matter what the pH/kH/CO2 chart shows. It just means you have something in the water that is lowering the pH.
17. I saw this electric method (like a Carbo-Plus) method of making CO2. Is it any good?
Short answer: NO. Long answer: Not a chance. Explanation: These units are almost as expensive or just as expensive to obtain as a pressurized system. They are much more expensive to run in the long term. They strip the kH out of your water to make the CO2. So your water chemistry is a ever changing target. They have a very hard time obtaining and maintaining decent CO2 levels (30 ppm). If you look around for a month or so you can almost always find one of these for sale used at a very deep discount. Yet you hardly ever see the same thing with a pressurized system. Kind of makes you wonder doesn't it?
18. Will the pH drop/rise from CO2 hurt my fish?
No it won't. When you add CO2 the pH should drop. If you use a timer to turn off the CO2 at night then the pH will rise. These changes in the pH do no harm to the fish. Now the reason this is so is that in real life when the pH rises or falls it's always accompanied by a change in the hardness and the TDS (Total Dissolved Solids) of the water. It's the changes in the hardness and TDS that can harm fish due to Osmotic Shock. Since the addition or removal of the CO2 changes neither the hardness or TDS it has on effect on fish.