updated May 2020
A good CO2 system is an often overlooked, but critically important part of a successful planted tank- one that supports good plant growth and allows one to grow carpets and more demanding species easily. The 'why' behind CO2 injection is explored in more detail here.
Above: a bouquet of green Syngonanthus 'Lago grande' against a red bush of Ludwigia sp. Red amongst other plants. Such density, form and coloration is not possible in a tank without CO2 injection. An overview of how to set up a CO2 system for the first time is covered in this article.
When it comes to CO2 systems, it is worthwhile to invest in a good regulator, in the same way that it is wise to go for a quality computer CPU: it is a sophisticated component that has a huge impact and hard to troubleshoot if problematic. For regulators, in the US, Green Leaf Aquariums has a great reputation. CO2 Art is another reliable brand.
Above: The pro-elite range by CO2 Art.
For a detailed guide to CO2 diffusion methods, go here. While in-tank diffusers are most common, the more reliable path is through an in-line atomizer. In-tank diffusers depend heavily on where and how it is placed within the water flow to get good CO2 distribution, while an in-line atomizer is more 'fail safe' in this regards. You want one that produces very fine mist rather than bubbles. This budget version, the NILOCG AQUATICS INLINE ATOMIZER works well enough.
If you do not want any CO2 mist, go for a CO2 reactor but be aware that reactors come in far more varied designs- some work well, many don't. It is important to match a reaction with the stated filter flow, otherwise its efficacy can be severely compromised. A example of one that works well from SERA is listed below.
CO2 diffusion is highly dependent on good water flow and a LILY PIPE such as the one below is particularly effective in directing water flow after it exits the filter pump. This design is elegant and helps circulate water from the surface to the bottom, an important aspect of improving gaseous exchange. This allows better CO2 distribution, better oxygenation and allows you to 'overload' CO2 safely, as described in more detail here.
Another device that improves water flow and thus CO2 distribution is a surface skimmer. A surface skimmer like the model from KOLLER listed below helps to improve gaseous exchange, which is essential for increasing CO2 levels safely. Such a device is standard in all 2Hr TanksTM.
Bubble counters are useful for checking the flow of CO2. The RHINOX CO2 BUBBLE COUNTER below comes with an in-build check valve.
CO2 resistant tubing such as the one below by AQUATEK lasts longer than normal air line tubing and is more corrosion resistant.
Below is a summary of products I have used or have experienced to a degree that I'm fully comfortable to recommend. If you do buy the products through the Amazon links below, I do earn a small commission (at no extra cost to you) which helps in the running of this website. ~The 2Hr Aquarist