There’s nothing quite as lovely as a healthy planted aquarium filled with happy fish and vibrant plants.

And while you can have such an aquarium with very little equipment and limited work involved, there are definitely some devices and accessories you can add that will increase the value of life your plants, fish, and other critters have, without much extra work for yourself.

One of those devices is a CO2 for aquarium plants system.

Below, we’ll outline exactly how to choose the best aquarium CO2 system for planted tanks.

Best Aquarium CO2 System Quick-Find Table

  • Comes complete with everything you need to get started
  • Great for beginners
  • Easy set up and maintenance
  • Comes complete with everything you need to get started
  • Great for beginners
  • Easy set up and maintenance
  • Solid trio of device components for your best DIY CO2 system kit
  • Outstanding quality
  • Easy to set up with the rest of your DIY kit
  • Solid trio of device components for your best DIY CO2 system kit
  • Outstanding quality
  • Easy to set up with the rest of your DIY kit
  • Professional grade
  • Perfect for the DIYer looking to fully customize the CO2 system
  • Easy to use and understand the gauges, et cetera
  • Professional grade
  • Perfect for the DIYer looking to fully customize the CO2 system
  • Easy to use and understand the gauges, et cetera

What is a CO2 System and Why Would You Want One for Your Aquarium?

Live plants need two things to grow healthy and strong: light and CO2 (carbon dioxide).

fish in planted tank best co2 system for aquariums

CO2 is required for respiration by aquatic plants, and they use this along with the light to go through the process of photosynthesis.

They need a constant supply of this CO2 much like we need constant supplies of oxygen. They combine the water, CO2, and light to produce that oxygen we need and the sugars they need for growth.

In the wild, plants get CO2 from natural substrate like mud and decaying plant matter. But in an enclosed environment like an aquarium, they don’t have as much access to CO2 for their growth processes.

We work hard to remove substances from aquariums that might provide plants with these materials, so sometimes they really struggle to get enough CO2 to grow well.

So, simply put, a CO2 system is an injector system that adds CO2 to your aquarium environment for the enhancement of plant growth.

What Kind of Aquariums Need CO2 Systems?

Whether or not you need a CO2 injector or not depends heavily on the type of aquarium you keep, how much light your aquarium receives, and whether or not you use fertilizers and other materials to supply your aquarium with the proper nutrient sources.

The primary type of aquarium that would benefit from a CO2 injector or an automatic CO2 system aquarium setup would be a planted aquarium.

Reef tanks, marine tanks, and fish-only tanks rarely – if ever – need additional CO2 beyond what naturally occurs there.

And technically, planted aquariums do not require an aquarium CO2 system. If you want thriving, gloriously growing plants, however, you will find this easiest with such a system.

Low light aquariums are less likely to need a CO2 injector for plant growth stimulation. The break down of dead plant matter, fish respiration, and surface agitation are usually enough to provide the necessary CO2. However, the low light aquarium could still benefit from an aquarium CO2 system, it’s just not quite as vital.

When we start talking medium and high light aquariums, however, CO2 injection becomes nearly vital.

The more light that’s available to plants, the quicker they grow. The quicker they grow, the more they need CO2. To meet that need for the high demand of CO2, a fish tank CO2 tank system is practically mandatory.

Without it, your fish tank is likely to produce algae and have other similar issues.

Benefits of Using a CO2 System in Your Aquarium

There are a few specific things plants in any environment need to grow: CO2, soil – or at least the nutrients received through soil – and light. For aquariums without plants, CO2 systems aren’t particularly beneficial, but planted aquariums need the CO2 in most cases.

While our aquariums are not a natural setting for plants, we can do a few things to come closer to simulating that natural environment for them. One of those is providing them with higher CO2 or carbon dioxide to increase and improve growth rates.

planted tank with live plants and fish needs a co2 system

Low carbon dioxide levels aren’t very natural for your plants, so using the best aquarium CO2 system will give the planted aquarium an instant redirect towards a more natural environment. In their natural environment, plants ingest CO2 through the substrate provided by mud, decaying plants, et cetera. But since your aquarium is a small, closed ecosystem, you don’t have the luxury of leaving those elements in your substrate. In fact, if you do, your fish can become ill.

In your aquarium, the CO2 is naturally lower because the substrate imitates a natural landscape, rather than providing actual decaying plants, et cetera, and this throws off the balance. This imbalance affects the health of your plants.

Required Tools and Pieces for a Complete CO2 System for Aquarium Setup

There are several parts to your CO2 generator aquarium setup.

Most – or all – will come with your system when you purchase it, but for a better understanding of what you’re doing and what you’re getting into, here’s a short breakdown on the info on what’s involved and what to look out for in your aquarium CO2 system.

The CO2 Bottle

CO2 – or carbon dioxide – comes in several bottle sizes, similar to propane tanks you’d purchase for your grill or camping stove. And, not to be too obvious, but the larger the bottle, the more CO2 you get.

To save money on your CO2, you can look for wholesale sellers for long-term savings.


The solenoid acts as the system automation tool. This disables the injection of CO2 into the aquarium, based on an attached timer.

The solenoid makes your CO2 system for aquariums more self-sufficient and therefore easier to use and maintain over time.

If, for example, you’re away from home for a longer time than usual, the solenoid tells the system to turn off automatically. Less CO2, less stress for you.


The regulator is the portion of the system that acts as the injection tool. The regulator releases pressure from the bottle to lower and manage the output pressure.

Typically, a regulator comes with a gauge that allows you to monitor the rate of injection so that you can adjust and make the proper changes necessary for the right amount of CO2 into your aquarium.


The diffuser is the part of the system that inserts the CO2 into the aquarium. The diffuser is made from a porous material that injects the CO2 into the tank via a fine mist of bubbles.

It also functions to disperse the CO2 gas throughout the entire aquarium water so that it’s most effectively used by the entire plant colony in your fish tank.

Bubble Counter

The metric tool used to quantify the CO2 levels pushed into your aquarium is called the bubble counter. This part of the equipment is usually added to your filter.

It measures the rate of bubbles exported per second and helps you determine if your aquarium needs less or more carbon dioxide.

CO2 Drop Checker

A color-coded gauge measuring the concentration of CO2 in your aquarium water is the drop checker.

Unlike the regulator and bubble counter, the drop checker measures the rate of injection, giving you a clear understanding of CO2 saturation in your aquarium ecosystem. This provides a better understanding of the health of your aquarium.

Too much CO2 is unhealthy for your fish, but too little won’t help your plants grow.

CO2 Tubing

The final component of your aquarium CO2 system is the tubing. This tubing works as the connector between your regulator and diffuser.

It’s important to choose the right tubing, though, as not all tubing is created equal. Look for tubing that’s CO2 tolerant.

Types of Aquarium CO2 Systems

There are three basic types of CO2 systems that may or may not be suitable for your circumstances.

1. Manual CO2 Systems

Most manual CO2 systems basically function as yeast fermentation systems. CO2 is generates as a metabolic byproduct of yeast and is stored in the fermentation canister. The accumulated CO2 travels through a reaction chamber and then mixes with the aquarium water via the powerhead or diffuser.

Manual CO2 systems are suitable for smaller planted aquariums.

Semi-Automatic CO2 Systems

Semi-automatic CO2 systems require a bit more effort initially for installation but work from a timer-operated system to help simplify the process of injection.

The semi-auto system uses the solenoid, bubble counter, diffuser, and regulator to work through timer operated setup for a set period of time – such as when the lights in your aquarium are on – to supply the plants with carbon dioxide.

These systems are best suited for medium-sized and larger planted aquariums.

Automatic CO2 Systems

Similar to semi-auto systems, the fully automatic CO2 system uses the same components, but add in a pH controller and probe. The upgrade in technology constantly monitors the aquariums pH levels while the prove detects pH level drops below the set point.

If the difference is within specific parameters, the system automatically shuts off the CO2 flow to prevent further changes.

These systems work for aquariums of all sizes but especially benefit heavily planted or large aquariums.

planted tank with fish in a co2 system aquarium

Reviews of the Best Aquarium CO2 Systems

To find the best aquarium co2 system options available, we dug around the various online reviews from professionals and hobbyists alike before diving into our own research.

We culled through the list by knocking out obviously paid reviews and then used these elements to determine the best options available.

Then we did our own in-depth reviews and research on each aquarium CO2 system to determine the best choices for your aquarium setups. We looked at the following parameters when deciding on our top picks:

  • Trusted brand names – with a reputation for quality, durability, and customer service
  • Ease of use and maintenance – can pretty much anyone use it?
  • Value for the price – quality appropriate to the price range
  • Various tank and plant needs – multiple options for various setups
  • Type of material – glass, metal, acrylic
  • Low profile – to avoid messing with that important aesthetic
Fluval Pressurized CO2 Kit

For folks looking for a full CO2 system kit, all-in-one purchase, the Fluval Pressurized CO2 Kit is your best bet.

The kit comes with everything you need – so no additional expenses or hassles – and is super easy to set up and maintain throughout the life of your aquarium.

Here’s the breakdown:

  • System type: Pressurized CO2
  • Cost effective: Not the most budget-friendly
  • Best for: Small aquariums
  • Comes with: Everything required for a CO2 system, including 3 refill CO2 cartridges

What We Loved

The first and foremost thing we love about this kit is that it’s an actual kit. It comes with everything you need – the regulator check valve with gauge, disposable CO2 cartridges, ceramic diffuser, holding bracket, and connecting hose.

We love how easy this system is to set up, too. In fact, it’s just about the easiest one to set up on the market. This means it’s great for beginners as well as long-term aquarists who know they’re stuff but want to reduce the hassle.

We also love that this comes from a trusted company we’re happy to recommend on just about any product in the fishkeeping world. You’ll rarely find issues with their products, so it’s easy to place this one at the top of our list.

We love how powerful and efficient this kit is. The whole system is strong enough to push CO2 into your aquarium while being discreet and quiet.

What We Didn’t Love

The main issue we have with this one is that the Fluval kit is quite a bit pricier than a lot of the competitors.

The value difference, however, is pretty huge, so despite the cost difference, we can still recommend this as the number one pick.

Our Verdict on the Fluval Pressurized CO2 Kit

If you are looking for the simple set-up, all-in-one CO2 system kit, the Fluval Pressurized CO2 Kit is the way to go. It includes everything you need, is incredibly easy to set up, and it really does its job well.

The cartridges that the system uses last for a good while, and the brand is an ever-trusted company among fish keepers.

All around, it’s your best bet for a complete setup.

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#2. DoubleSun CO2 Regulator

DoubleSun Aquarium CO2 Regulator with Solenoid 110V-Mini Dual Gauge Display Bubble Counter

The DoubleSun regulator, solenoid, and bubble counter comes from a great brand that makes its devices with high-quality materials that are extremely durable and last a long time.

This particular selection of devices work well with most high-density tubing options, and work well with a number of CO2 diffusers and atomizers.

It’s a great, affordable option for those who want to DIY their own kit.

Here’s the breakdown:

  • System type: Various
  • Cost effective: Great value
  • Best for: Medium to large aquariums
  • Comes with: CO2 regulator, solenoid, bubble counter

What We Loved

While this isn’t a full kit, we still love the combination of devices that come together in this partial kit.

The trio combination is perfect for folks looking to DIY their own CO2 system for the perfect setup for their specific aquarium needs.

We love that the kit provides devices that are compatible with most high-pressure tubing, diffusors, and atomizers, meaning this collection really is a great option for DIYers.

We love the easy adjustability settings with the wide range of 150 to 250 psi. And we love that the display that comes with the devices is extremely easy to read and understand for the best, most precise CO2 delivery possible.

We also love that this kit performs consistently and reliably throughout its lifetime. Can’t beat that. The reliability is seriously one of its best features. Folks praise it everywhere for its ability to keep up and keep going. Just get the settings right and you’re good to go.

Finally, we love how energy efficient the solenoid is. It’s super quiet, runs at a low temperature – meaning no disturbance to the fish or plants – and all of that also means it helps extend the life of the regulator.

What We Didn’t Love

There are only two real issues we’ve noticed with this CO2 system kit.

First, the instruction that come with it are rather difficult to understand. We highly recommend Googling an instructional video instead of trying to follow the confusing directions.

The second thing is that the bubble counter doesn’t rotate. If you need it in a different position, you’ll have to acquire an additional stand. It’s far from the end of the world, but it is a bit annoying.

Our Verdict on the DoubleSun Regulator, Solenoid, & Bubble Counter

Overall, this is the best kit for DIYers.

It provides you with three components for your CO2 system for planted aquarium, that work with just about any setup you could create through other acquisitions. It’s powerful, durable, reliable, and incredibly effective.

The only real downside is that the bubble counter doesn’t rotate, so you might have to acquire an additional stand to position it just so.

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S.T. International Aquarium 2-Gauge Professional CO2 Regulator

The S.T. International Aquarium Professional CO2 Regulator is built with a decompression pressure gauge that easily adjusts, giving a steady and precise CO2 yield in your aquarium. It includes a professional grade solenoid valve, is extremely energy efficient and effective flow that works discreetly.

It’s quiet, doesn’t add heat to your aquarium, and it’s built to last.

Here’s the breakdown:

  • System type: Any
  • Cost effective: High-end cost
  • Best for: Medium and larger aquariums
  • Comes with: Regulator, pressure gauge, solenoid valve

What We Loved

We love how great this is for the custom CO2 aquarium kit. It offers some beneficial components without being paired with options you might not want.

We also love that it comes equipped with an all-inclusive voltage rating for global use, with PSE and CR accreditation along with International Patent endorsement for ultimate safety. And you can use small or large US barrels of CO2 with the system without problem.

We also love that the pressure gauge uses the rainbow colors, but that you can personal the preferences for the most readable output for your situation.

You can easily adjust the number of bubbles using this regulator, and it’s quiet and energy efficient.

It’s also solidly built and made to last for a long, long time.

What We Didn’t Love

There are only two potential downsides to this regulator.

The first is that has an uncommon washer size, so replacements can be a headache to find.

The second is that there is no light indicator letting you know if it’s on or off. While everything else is great, that’s kind of a big one for us, which is why this ranks lower down.

Our Verdict on the S.T. International Aquarium Professional CO2 Regulator

All in all, the S.T. International Aquarium Professional CO2 regulator is a fantastic option for anyone looking to custom build their CO2 system.

They’re easy to use and read, energy efficient, quiet operators, and extremely versatile.

The only real downsides are a lack of light indicator – power on/off – and the fact that the washers are an uncommon size and therefore difficult to replace, if needed.

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