This is Part 1 of our multi-part guide to CO₂ systems for planted aquariums. It was originally written for The Current, our Blue Zone Aquarium blog, but since our site is undergoing extended updates, we’re publishing the series here.
⚠️ Safety Reminder
Never install a regulator onto a cylinder with an open valve — always make sure it is closed.
Before installing a regulator onto a new CO₂ cylinder, make sure all of your needle valves (on the regulator and any splitters or manifolds) are fully closed. Many regulators and accessories come from the factory with their valves wide open, and if left that way you can lose gas immediately when you open the cylinder.
Do not plug in your regulator’s solenoid until your full system is connected, tightened onto the cylinder, and all bubble counters, splitters, and tubing are properly attached. If the solenoid opens while the regulator is only partially seated, CO₂ can exhaust into the atmosphere — wasting gas or blowing the fluid out of your bubble counters.
Why Add CO₂?
Adding CO₂ is one of the most effective upgrades for a planted aquarium. It drives faster, healthier growth and lets you keep more demanding plant species. Before you start dialing in bubble rates and timers, you need the right gear — plus a few practical tips that will save you time, money, and frustration.
Essential Equipment Checklist
- CO₂ cylinder (2½ lb, 5 lb, 10 lb, or 20 lb)
- Regulator with solenoid and bubble counter
- CO₂-rated tubing
- Check valve
- Diffuser, atomizer, or reactor
- Drop checker (not required but recommended — covered in Part 2)
Our Recommendation
For most aquariums, you’re better off with a standard pressurized CO₂ system: a regulator and a refillable cylinder. Small starter kits and DIY bottles may look affordable at first, but they’re unstable, require constant refilling, and end up costing more long-term.
Even a basic single-stage regulator on a 2½-lb cylinder is a solid starting point. Premium regulators add finer needle valves, dual-stage bodies, sturdier fittings, and long-lasting solenoids — but a budget setup is enough to begin.
Choosing the Right Cylinder
Cylinder size doesn’t change how the system works, but it does determine how often you’ll need a refill.
- Small tanks (up to 20 gal): A 2½-lb cylinder can last for months.
- Medium tanks (20–55 gal): A 5-lb cylinder balances footprint and refill frequency.
- Large tanks (55+ gal): A 10- or 20-lb cylinder saves refill trips and cost over time.
💡 Tip: Many welding shops let you “upgrade” cylinders. Start small, and when you exchange, you can often pay the difference for a larger size — making the move more affordable.
New vs. Used Cylinders
New from a gas supplier
- Usually more expensive.
- Many suppliers swap bottles instead of refilling yours.
Owning your own cylinder
- Only possible if your local supplier does on-site refills.
- Check refill policies before paying extra for a branded tank.
Used cylinders
- Great deals exist, but check the hydrostatic test date (valid for 5 years in the U.S.).
- If expired, you’ll need a retest before refilling.
Regulators Explained
A regulator reduces cylinder pressure to steady working pressure and lets you fine-tune flow.
Single-stage vs. dual-stage
- Single-stage regulators are cheaper and common. They can “dump” a final burst at the end of a cylinder.
- Dual-stage regulators prevent that, making usage more stable and predictable.
Needle valves
- Older budget regulators had poor valves.
- Modern ones (even affordable) usually hold steady.
- Premium valves give smoother control.
Gauges
- High pressure: shows cylinder pressure (~800–1000 PSI full).
- Low pressure: shows output to your diffuser/reactor.
Working pressure ranges
- 10–15 PSI: Reactors
- 20–25 PSI: Ceramic/glass diffusers
- 30–40+ PSI: Inline atomizers
- 40+ PSI: Multi-tank systems with splitters
Solenoid
- An electronic valve, timer-controlled, so CO₂ only runs during the photoperiod.
CO₂ Splitters and Manifolds
- Splitters: One-piece blocks with 2–6 arms, each with its own valve and bubble counter. Cost-effective and practical.
- Manifolds: Modular add-ons, brand-specific, and usually more expensive but guaranteed to fit.
💡 Always check for O-rings on fittings. Missing seals are a common cause of leaks.
Bubble Counters
Regulator-mounted
- Attach directly to the regulator.
- Use the included O-ring or leaks will occur.
Inline bubble counters
- Mounted away from the regulator.
- Easier to read and service.
Fluids
- Best: Vegetable glycerin (safe, clear, stable).
- Avoid: Water (evaporates, needs constant refilling).
Always open needle valves slowly to avoid foaming the counter fluid.
Tubing
Always use TPU CO₂ tubing, not airline tubing. TPU is:
- Gas-tight (won’t bleed CO₂).
- Durable (resists cracking).
- High-pressure rated.
Tips
- Use elbows/U-bends for tight corners.
- Warm tubing in hot water before attaching to delicate glass parts.
Check Valves
Prevent water backflow into your regulator.
- Install at least one, even if your bubble counter has one built in.
- CO₂ check valves are designed for higher pressure; airline valves won’t work reliably.
Diffusers, Atomizers, Reactors
- Diffusers: Simple, inside the tank, work at 20–30 PSI.
- Atomizers: Inline, outside the tank, fine mist, higher pressure needed.
- Reactors: Highly efficient, best for large tanks, no visible bubbles, but bulky.
👉 For most aquariums, a diffuser is the most reliable and simplest choice.
Conclusion
DIY kits and cartridges can work, but they’re unstable and costlier over time. A pressurized cylinder with a regulator is consistent, controllable, and more economical.
This completes Part 1: Equipment & Considerations.
Next up: Part 2 – Setup & Adjustment
We’ll cover installation, setting working pressure, bubble tuning, drop checkers, and simple leak tests.