Tips by Dou Mok, Felix Smart Ambassador
If you're starting a freshwater planted tank, you will inevitably run into the question - do I need CO2 to grow plants? The short answer is no - you actually don't need CO2 to grow plants. The long answer is not for dummies - so I'll leave that to the experts* to discuss. However... "no" doesn't mean that all plants can't benefit from CO2 injection. So, what do you really need to know?
Buy things once, right - not twice.
There is no question that you should consider buying and setting up a CO2 system if you are serious about growing plants underwater. There are various options out there, but the one I recommend is the option that involves a CO2 Cylinder and a Regulator with Solenoid. Do your research and buy products from reputable brands so that you can focus your attention on your tank and plants. Injecting CO2 is something you will want to put on a schedule and automate so that you don't have to manually turn on and off (Use the FelixSmart's Range feature!).
Take things slowly at your own pace.
It might be tempting to add a lot of CO2 in your tank at first because you want your plants to grow fast, but adding CO2 does not come without it's own complexities. With any new element that you add into your tank, you should take things slowly so that you can observe the changes. Start with 1 bubble per second and see what happens after a week. If you have many plants, consider starting with 2. Make sure that your CO2 bubbles are being spread all throughout your tank - this might mean moving your CO2 diffuser underneath your outflow! If your tank is one that develops an oily film on the surface, add a skimmer and set that on a timer (use the Felix Smart's Range feature!). If you have fish, they will appreciate you giving them some time to get used to the CO2.
"The Water Tests" vs. "The Eye Test"
How does one find out if one's tank has enough CO2? You can either test your water parameters (pH/kH) or do an eye test. The eye test is about confirming that your plants are growing by observing whether you see pearling (photosynthesis) or not. George Farmer* describes this best - it happens when plants have the food they need to grow so well that they start to form visible bubbles of oxygen on their leaves. You should be able to observe this happening within 2 hours of your lights turning on if you inject CO2.
If you really want to get into this more, I'll leave you with some verbiage from Tom Barr**: "Adding CO2 increases photosynthesis 10-20X normal rates without adding it, thus the O2 is produced at a much higher rate. This leads to more pearling due to O2 production by the plants. Oxygen is pretty insoluble in water to begin with, CO2 is not. Try and get 50 ppm of O2 into your tank's water sometime. Water is equilibrated with air at 100%(say 7 ppm at 28C), but it's so "saturated" that O2 forms into bubbles and pearls away."
The water test is not for dummies so if you're ready to challenge yourself, here is some advice from Dennis Wong***, author of "Advanced Planted Tank": "As a very general guide, if you have KH values between 1 - 10 dKH, aim for a 1 point relative pH dropfrom the point when CO2 injection is not yet turned on to the time after it has been turned on and CO2 has risen to a high, stable equilibrium point."
If you have a Felix Smart, you can easily monitor the pH through the App as a rough way to gauge your CO2 levels. Practical.
Remember, every tank is different just like we are as humans. The right answer is the one that works for you and your plants - don't feel pressured into doing something that you don't feel comfortable with (or at least do your research!).