Equipment guide
CO2 Injection
Whether you actually need CO2, and how to run it safely if you do.
By Mike Elmira
TL;DR, CO2 Injection
CO2 is the single biggest lever for demanding plants, but it is optional, not compulsory. A low-tech tank of anubias, ferns, crypts and mosses grows fine without it. Carpets, red stems and fast lush growth really want it. If you inject, use a drop checker and aim for green, ramp the bubble rate up slowly over days, turn the gas on an hour or two before the lights and off before lights out, and never let it climb far enough to gas the fish. Stability matters more than a high number.
Running CO2 safely
- Drop checker blue
- Too little CO2, raise it slowly
- Drop checker green
- The target
- Drop checker yellow
- Too much, dangerous, cut it back
- Timing
- On 1 to 2h before lights, off ~1h before lights out
Do you need CO2
No, for a low-tech tank built around easy plants. Yes, if you want a tight carpet, deep reds, or fast dense growth. The honest middle path is to pick plants that suit whether you will inject or not, rather than fighting demanding plants in a tank with no CO2, which is a reliable route to algae and melt.
Methods
Pressurised CO2 from a cylinder and regulator is the proper way, steady and controllable. DIY yeast bottles are cheap but drift and run out, so they suit only small tanks. Liquid carbon products are not true CO2 and give a modest boost at best, though they double as a spot treatment for algae. For anything beyond easy plants, pressurised is the one that works.
Dialling it in
A drop checker with 4 dKH reference fluid is your gauge. Blue means too little CO2, green is the sweet spot, and yellow means too much, which is dangerous for livestock. Start low, raise the bubble rate a little each day, and watch the fish. If they gasp at the surface, back off at once.
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Do I need CO2 for a planted tank?
Not for easy low-light plants like anubias, java fern, crypts and mosses. You do need it for carpets, red stems and fast lush growth. Pick plants that suit whichever way you go.
Is CO2 dangerous for fish?
It can be if you overdo it. Too much CO2 starves fish of oxygen, which is why the drop checker turning yellow is a warning. Ramp up slowly, keep it green, and turn it off before lights out.