Pressurised CO2 kit for planted aquarium

The bubble counter on the diffuser provides a visual reference, and the non-return valve protects the regulator from water back-flow. Adjust the flow rate by a few bubbles per minute, then allow the permanent test to respond before making further changes. A CO2 setup stabilises over several days, not in a single evening. The plants that benefit most are fast-growing ones, and they also need light and nutrients, without these, carbon alone will do very little. Allow a good week before judging a setting, and note down every change you make; a three-line log will stop you going back and forth between two similar values.

The size should be chosen based on the actual volume of your aquarium, after deducting décor, not the volume printed on the original packaging. A tank rated at 240 litres filled with rocks and sand often holds around 200 litres of water, and it is this figure that matters. Two other criteria then come into play. First, planting density: a heavily planted tank consumes more CO2 at an equivalent volume. Second, autonomy: a larger bottle on a small tank makes no difference to the regulator setting, but noticeably extends the time between refills, which is a genuine advantage when the bottle is tucked away at the bottom of a hard-to-reach cabinet.

The life of a cylinder depends on the flow rate set and the daily injection period, not on the volume of the tank. A disposable 500 g cylinder typically lasts a few months on an average tank set at a sensible flow rate, and a solenoid valve extends that by a good third by cutting off the supply overnight. A refillable cylinder is topped up at a gas supplier, which works out considerably cheaper per gram but requires dropping it off and collecting it. Plan your refill before you run out, as a tank accustomed to CO2 reacts noticeably to an interruption of several days, with algae taking advantage of the imbalance. Note the start date on the base, and order the next fill when the bubble counter starts needing a wider opening to maintain the same flow rate, a sign that the pressure is dropping.

On an aquaponics circuit, this equipment has no place, as it is designed for a planted ornamental aquarium. The balance of a food-producing system depends on pH and the nutrients supplied by the fish, not on gas injection. Adding CO2 to water that feeds growing beds would also lower the pH at precisely the moment when the biofilter bacteria work best in slightly alkaline water, which would amount to disrupting filtration in order to feed plants that grow above water and draw their carbon directly from the air.