1. What you need
A cylinder system is made of a few parts that work together. CO2 comes from the cylinder through a regulator, then along CO2-resistant tubing through a check valve and a bubble counter to a diffuser, which dissolves the gas in the water. For a small tank the Tropica CO2 System Nano is a ready kit: a disposable aluminium cylinder with 95 g of CO2, a regulator and a 3-in-1 diffuser.
For a larger tank you choose the regulator separately, for example the CO2Art Pro-SE, a dual-stage regulator with an integrated solenoid valve. The dual-stage construction keeps the working pressure steady as the cylinder pressure drops and prevents an end-of-cylinder dump.
2. Tubing, check valve and bubble counter
Use CO2-resistant tubing: the wrong material turns brittle and leaks gas. The CO2Art 4/6 mm polyurethane tubing fits CO2Art glass diffusers, and the maker suggests dipping the end in boiling water for two seconds to fit it onto glassware.
A check valve lets CO2 flow one way only and protects the system, above all the solenoid valve, from water flowing back. A bubble counter shows how much CO2 is flowing: counting bubbles per minute gives an easy estimate. The Tropica 3-in-1 diffuser combines a bubble counter, a reflux valve and a ceramic diffuser in one unit.
3. Installation step by step
First attach the regulator to the cylinder. Because the gas is under pressure, Tropica advises protecting your hands, for example with an oven glove or a towel, when you mount the regulator. Then connect the tubing to the regulator outlet and its other end to the bubble counter or the 3-in-1 diffuser.
Place the diffuser in the tank where the flow carries it well and fix it with the suction cup. Put the check valve between the regulator and the diffuser so water cannot rise back into the tubing. Before opening the cylinder, check that all connections are secure.
4. Start-up, timing and drop checker
Start with a low flow and raise it slowly over several days, not all at once. Follow the manual of your kit and watch the bubble counter. A drop checker helps you judge the level: the CO2Art drop checker solution shows green as right, blue as too little and yellow as too much. The colour change takes time, so do not adjust the setting every hour.
Switch CO2 on about an hour before the light and off about an hour before the light goes out, because plants do not use CO2 in the dark. A solenoid valve and a timer make this automatic.
5. Safety and watching the fish
Watch the fish carefully in the first days. If they gasp near the surface or behave unusually, reduce CO2 at once and let the tank recover with fresh water or aeration. Never raise the dose when the fish are already stressed.
Remember that the effect of CO2 depends on tank size, plant mass and light. A setting that suits one tank can be too strong in another. Always change only one thing at a time and wait at least a day before the next step to see the result.
Keep the cylinder upright and firmly secured, away from heat, and do not use damaged tubing. If you doubt how the system is working, close the cylinder and check the connections. See also the guide to water tests if you want to monitor the water.
Parts of a CO2 system and what they do
| Part | What it does | Note |
|---|---|---|
| Cylinder | CO2 supply | Tropica Nano: 95 g, disposable |
| Regulator | keeps pressure steady | Pro-SE: dual stage |
| Tubing | carries gas to the diffuser | CO2-resistant 4/6 mm |
| Check valve | stops water flowing back | protects the solenoid valve |
| Bubble counter | shows flow | bubbles per minute |
| Diffuser | dissolves CO2 in the water | Tropica 3-in-1 |
| Drop checker | shows the level by colour | green, blue, yellow |
Checklist
- Choose a system by tank size.
- Use CO2-resistant tubing, not ordinary tubing.
- Put the check valve between the regulator and the diffuser.
- Mount the regulator on the cylinder with your hands protected.
- Start with a low flow and raise it over several days.
- Switch CO2 on about an hour before the light.
- Watch the fish and check the level with a drop checker.
Products for this guide
Frequently asked questions
How long does a Tropica nano cylinder last?
Tropica notes the nano cylinder holds 95 g of CO2, but in a larger tank with more demanding plants it will not last long. Duration depends on tank size and setting.
What do the drop checker colours mean?
By the CO2Art description green is right, blue too little and yellow too much CO2. The change takes time, so do not rush.
Do I need a solenoid valve?
Not necessarily, but together with a timer it switches CO2 on and off automatically. The Tropica CO2 System Nano description lists a cylinder, a regulator and a 3-in-1 diffuser.
Does a beginner need CO2?
Not necessarily: many undemanding plants grow without CO2. Tropica recommends System Bio for starter aquariums up to 60 L and System Nano for nano aquariums.
