The CO2 pressure gas cylinder

The CO2 pressure gas cylinder (simply CO2 depot) I use is of the brand Dupla and is supplied with a armature Delta (see picture on the right), which is  a piston type regulator, that decreases the CO2 to a 1 bar output pressure. The CO2 depot has a capacity of 500 gram CO2. I've chosen for a CO2-fles of this brand because it can be filled in the store. This can't be done with for example the CO2 depots of Sera, which have to be sent to another place to fill them which can take a few days. Therefore you can't uses you CO2-system for several days unless you've got a spare depot. Because the CO2 depots of Dupla can be filled in the store you can you don't need a spare bottle because the CO2-fles can be filled almost immediately. Before you go to the store with the empty CO2 depot to let it fill you have to put it for at least 5 hours in the freezer otherwise it can't be filled for the full 100%. After you have removed the armature of the CO2 depot, it's wise to put some vaseline on the rubber of the armature to prevent it from damaging.

The CO2-basic set

The CO2 basic set I use is of the brand Sera (see picture on the left). This set contains the following parts: a CO2 reactor, a bubble counter, a C02 indicator, a T-piece for connecting the CO2 reactor with the filter and some hoses. Although this set is of a different brand than the CO2 depot I use everything fits well on each other because both brands uses the same size of hoses. The reason why I've chosen for the set of Sera is because this  set was much cheaper than the comparable set op Dupla. Although Dupla offers an even cheaper alternative then Sera when you choose for a CO2 diffuser (see picture on the right) which is for use in small aquariums, I still prefer the reactor of Sera (for aquariums up to 300 liters). This because even with a reactor I still have to use a lot of CO2 for decreasing the pH value to the preferred pH 7.0. 

The pH regulation set

The pH regulation set I use contains a magnet valve (see picture on the left) and a pH-control Delta (see picture on the right), both of the brand Dupla. Although I've used CO2 addition without pH  regulation for a long time without problems, I still decided to regulate it by pH regulation a few months ago. The reason of this I now try to explain. 

The main difference between an not regulated and an regulated CO2 addition is that when no regulation is used the pH value of the water will start at for example 7.0 in the morning and shall increase till for example to 7.5 at the end of the day. At night the pH value will decrease again to pH 7.0. When a pH regulation is used the pH value of the water shall vary between 0.1 and 0.2 pH of the set point at all times. My opinion is that this helps to give the aquarium a stable environment. This is the reason why I decided to regulate the CO2 addition through pH regulation. 

Although the display of the pH regulation gives a pH accuracy of 0.01, I think the value of 0.1 as mentioned in the instruction manual is not even reach. For a while I've though that this was because of the temperature of the calibration solution because this has to have the same temperature as the aquarium water temperature. I myself think that the reason of the bat accuracy of the pH measurement of the pH regulation is because of a combination of a number of factors like quality of the pH electrode, accuracy of the electronics, temperature of the calibration solution and the accuracy of the calibration solution. These factors taken together give the pH measurement a pretty large inaccuracy in my opinion. Therefore I myself use a regular pH test (Dupla pH 6) to give my CO2 regulation the right settings, because I myself think this test is much more reliable than the measurement of my CO2 regulation set. Therefore my pH regulation is set on a value of pH 6.85 while the "through" pH value of my water is around the pH 7.1. More about electronic pH measurement can be found on the Belgium Internet site The aquarium guide, that also can be found on the links page. 

General things about CO2 addition

As probably known by you circulation of the water drives out the CO2 in the water. Especially circulation on the surface of the aquarium drives a lot of CO2 out of the water. Therefore the water circulation has to be as less as possible. Therefore is a air diffuser in an aquarium with CO2 addition is out of the question. Also it's wise to place the outlet of the filter not directly under the surface but a bit deeper into the aquarium. In my aquarium I clearly can see the influance of water circulation at the surface through the surface suction extractor on my filter I use. This also gives some water circulation on the surface. When I'll let this surface suction extractor clean the surface for 24 hours a day the CO2 use of the aquarium is noticeable higher than when I only use it for some hours a day. This example makes clear that even a little increase of water circulation at the surface of the aquarium let's to bigger demand for CO2 in the aquarium.