ADA · Diffuser
Pollen Glass Beetle
Pressurised CO2 tanks where you want a neat, nearly invisible diffuser and are happy to clean glass now and then.
3 models
Gear catalogue · 19 co2
Aquarium co2, compared properly
Regulators, diffusers, drop checkers and complete kits. From ADA, Qanvee, Twinstar, UNS. Match them to your tank, then put up to four side by side.
TL;DR, choosing aquarium co2
Pressurised CO2 is the single biggest upgrade for plant growth, and the parts are simpler than they look: a cylinder holds the gas, a regulator drops the pressure and a solenoid turns it off at night, a needle valve and bubble counter let you set the rate, and a diffuser or reactor dissolves it into the water. A drop checker then tells you roughly how much is in the tank. Dual-stage regulators hold a steadier output as the cylinder empties, which avoids the dreaded end-of-tank dump. Match the diffuser to your tank size, or go inline on the canister outlet for a cleaner look. Always put a check valve between the tank and the regulator.
How to choose
- Start with the regulator. Dual-stage with a solenoid is the safe long-term choice.
- Match the cylinder fitting to the regulator (paintball, CGA320 or disposable cartridge).
- Size the diffuser to the tank, or fit an inline diffuser on the canister outlet.
- A drop checker is cheap insurance. Aim for lime green by lights-on.
ADA · Diffuser
Pollen Glass Type 3
Small to medium pressurised CO2 tanks where an upright glass diffuser suits the look.
1 model
ADA · Regulator
PS-SC Speed Controller
Keepers running pressurised CO2 who want finer adjustment than their regulator gives, or split lines to two tanks.
1 model
Qanvee · Diffuser
Inline CO2 Atomizer
Planted tanks with a canister filter, especially 190 L and up, where you want hidden CO2 hardware.
2 models
Twinstar · Diffuser
CO2 Diffuser
- Tank size
- 121–121 L
Small to large planted tanks where you want a tough, tidy in-tank diffuser with the bubble counter included.
3 models
UNS · Cylinder
CO2 Cylinder Pro
Anyone running a Pro or Mini regulator who wants the lowest running cost per fill.
4 models
UNS · Diffuser
CO2 Diffuser
- Tank size
- 197–197 L
Any pressurised CO2 tank where you want a simple, low-cost in-tank diffuser.
3 models
UNS · Cylinder
CO2 Paintball Cylinder
Small to medium tanks where a full-size cylinder will not fit in the cabinet.
2 models
UNS · Drop checker
Drop Checker
Anyone running pressurised CO2 who wants a simple visual check.
2 models
UNS · Bubble counter
Micro CO2 Bubble Counter
Fine-tuning bubble rate on any UNS regulator, or as a spare.
1 model
UNS · Complete kit
Micro CO2 Kit
Nano and desktop planted tanks where you want timed, pressurised CO2 on a small budget.
1 model
UNS · Regulator
Micro CO2 Regulator
Desktop nanos where every centimetre of space around the tank counts.
2 models
UNS · Regulator
Micro CO2 Solenoid
Anyone already running the Micro regulator who wants CO2 on a schedule.
1 model
UNS · Regulator
Mini CO2 Dual Stage Regulator
Nano and small tanks, especially if you might switch from cartridges to a refillable cylinder later.
1 model
UNS · Complete kit
Nano CO2 Kit
Tanks of roughly 4 to 40 litres where you want dual-stage stability without a large cylinder.
1 model
UNS · Complete kit
Paintball CO2 Kit
Small to medium planted tanks where cartridges run out too fast but a full-size cylinder will not fit.
2 models
UNS · Regulator
Pro CO2 Dual Stage Regulator
Medium to large planted tanks and fish rooms running refillable cylinders.
1 model
UNS · Complete kit
Pro CO2 Kit
Medium to large high-tech tanks, or several tanks fed from one cylinder.
4 models
UNS · Diffuser
Pro Inline CO2 Diffuser
Canister-filtered CO2 tanks where you want a clean, equipment-free look inside the glass.
3 models
Frequently asked questions
Straight answers to the questions people ask most when choosing aquarium co2.
Do I need a CO2 system for a planted tank?
No, plenty of beautiful tanks run without it on low-light plants. You need CO2 when you want high light, dense carpets or demanding red stems. Without it, strong light mostly grows algae.
Single-stage or dual-stage regulator?
Dual-stage if you can. A single-stage regulator can release a burst of gas as the cylinder runs low, which can gas fish overnight. Dual-stage holds a steady output right to the end.
Which CO2 diffuser should I buy?
One rated for your tank volume, placed low near the filter outlet so the mist circulates. On larger tanks an inline diffuser or reactor on the canister outlet dissolves more gas and keeps the glass clear.
How do I know how much CO2 is in my tank?
Use a drop checker with 4 dKH reference solution. Blue means too little, lime green is about right (around 30 ppm) and yellow means too much. Watch the fish as well: gasping at the surface means turn it down.
Other gear
Specs come from the maker or a major retailer’s listing and are checked where we can. Makers revise products, so confirm the figures on the product page before you buy. Product photos are supplied by the brands and their distributors.