Buyers Guides

A Guide To CO2 Diffusers

One of the key contributing factors to achieving lush and healthy plant growth is providing an available source of carbon dioxide (CO2). As plants utilise CO2 during the process of photosynthesis it is important to inject additional source of CO2 into the water column to achieve the best results from your plants, both in  terms of lush, compact growth and vibrant colouration.

The most reliable and controllable method of CO2 injection is from a pressurised system. A key component of CO2 equipment for your system is the diffuser. The diffuser is the piece of equipment which the CO2 passes through when being transfered from the CO2 cylinder into the water column of your aquarium. They are usually made of a porous ceramic plate or disc which will break the CO2 gas down into tiny micro-bubbles which can then be easily extracted from the water by the plants.

There are two main types of CO2 diffuser; inline and in tank.

Inline diffusers are inserted into the return hose of your external canister filter or sump. These are the most efficient diffusers as the CO2 bubbles produced get distributed around the tank by the direct flow of the filter, enabling every plant in the aquarium to have ready access to the CO2. This is especially important for larger tanks with a volume over 200 litres. The downsides to an inline diffuser is the visual presence of the micro-bubbles in the water column, giving a slight misty appearance to the aquarium. Whilst this is minimal it maybe enough to put some people off. Another factor to consider is the extra hose join in your filter pipework. This needs to be accessible for cleaning and maintenance.

We recommend the CO2 Art inline diffuser, a tried and tested piece of equipment with fantastic CO2 dissolution capacity.

In tank diffusers are placed inside the tank where the CO2 is diffused directly into the main water body of the aquarium. Being in plain sight, in tank diffusers are often constructed from clear glass or plastic and are designed to give a clean and stylish aesthetic. Placement of the in tank diffuser is key. The aim is to get the CO2 bubbles dispersed around the tank as evenly as possible, this is usually achieved by placing the diffuser on the side of the glass directly opposite the outlet of your filter. Keep a close eye on the bubbles, if they are rising straight to the top they will not be in the water long enough to be utilised by the plants. Move your in tank diffuser to a different spot to catch the water movement so the bubbles are “blown” around the tank.

When injecting CO2 you will be aiming for 20 – 30ppm of CO2. A good way to keep an easy watch on your CO2 levels is to install a dropchecker. These contain a liquid which measures a drop in PH. As the CO2 levels in the water increase the water become more acidic thus causing the PH to drop. The colour of your drop checker should turn from blue, to green, to lime green. If it turns yellow you are likely adding too much CO2 and should dial it down at the regulator. Lime green is usually a good colour to aim for. It is important to observe the behaviour of your livestock when increasing CO2. If you notice your fish swimming near the surface or gasping then quickly reduce the CO2 back down to safe levels. Position your dropchecker at the opposite end of the tank to your diffuser for the most accurate reading. Sometimes placing nearer the substrate will avoid giving a deceptively high reading.

When choosing a CO2 diffuser aim to pick the right size for your tank. Too small and you may have to force too much gas through which would result in larger bubbles being produced and could damage the diffuser over time. Too large and you may not get an even dispersion of bubbles across the ceramic plate at low pressures, as well as the diffuser looking large and cumbersome in the tank. Choose a diffuser with a rating appropriate for the volume of your aquarium.

The Twinstar CO2 diffuser is small and stylish.

For smaller and nano aquariums we recommend the Twinstar range of CO2 diffusers. These come in three different sizes: L – for tanks up to 250l. M – for tanks 60 – 100l. S – for tanks 60l and under. These pretty little diffusers look stylish, minimalist and modern, as well as being functional and efficient.

Another recommendation would be the CO2 Art Flux diffuser. Whilst not as pretty as the offerings from Twinstar and Seachem they are fantastically efficient and will produce incredibly tiny bubbles of CO2. We recommend the Flux diffuser in size large for higher volume tanks where fitting an inline diffuser isn’t possible.

The Flux diffuser from CO2 Art is less pretty but very efficient. (Now sold in brown colour).

Maintaining your CO2 diffuser is very important. A build up of algae on the diffusion plate can dramatically decrease the functionality and efficiency of the diffuser which will cause CO2 levels in the water to fluctuate, leading to poorer plant growth and algae. To clean the CO2 diffuser, remove from the tank and soak in a thin bleach solution for 10 – 20 minutes. Rinse throughly and then soak in a solution of dechlorinator (we recommend Seachem Prime), this will deactivate any remaining bleach on the diffuser. It is important to avoid touching the diffuser disc as much as possible as this can damage the surface.

Over time the diffusion plates can become damaged and less efficient. Products such as the CO2 Art IO diffuser and CO2 Art inline diffuser have the capability to replace the discs when they get worn, damaged or too dirty to properly clean. This is a great feature which means you can also have two or more replacement discs to hand, making maintenance a much easier and efficient task.