Do I Need CO2 for a Planted Tank? Honest Answer

Table of Contents

• The Honest Answer
• What CO2 Actually Does for Plants
• When You Do Not Need CO2
• When You Definitely Need CO2
• Decision Flowchart
• The Liquid Carbon Middle Ground
• Cost of a CO2 Setup in Singapore (SGD)
• CO2 System Components Overview
• Singapore-Specific Factors
• Frequently Asked Questions

The Honest Answer

Do you need CO2 for a planted tank? No, not for many setups. A low-tech planted aquarium with easy plants, moderate lighting and basic fertilisation can look absolutely stunning without a single bubble of injected CO2. Some of the most beautiful aquariums in the world are low-tech tanks that rely entirely on naturally dissolved CO2 from fish respiration and atmospheric exchange. This guide sits inside our broader Planted Tank Complete Hub reference.

However, if you want to grow carpeting plants, demanding red species or push your tank towards competition-level aquascaping, then yes, CO2 becomes essential. Without it, these plants will either grow painfully slowly, lose their colour or simply melt away.

The question is not whether CO2 is “good” or “bad” for planted tanks. It is whether your specific goals require it. Let us work through that decision.

What CO2 Actually Does for Plants

Carbon dioxide is the primary building block of plant growth. Through photosynthesis, plants use light energy to combine CO2 and water into sugars (energy) and oxygen. Carbon accounts for roughly 40-50% of a plant’s dry mass, making it the single most important nutrient.

In nature, rivers and streams have CO2 levels of 10-30 ppm from decomposing organic matter and soil interaction. A typical aquarium without injection has only 2-5 ppm of dissolved CO2. That is enough for undemanding plants but a bottleneck for species that photosynthesize rapidly.

Injecting CO2 raises the concentration to approximately 30 ppm, which is the sweet spot for most aquatic plants. At this level, carbon is no longer the limiting factor, and growth is determined by light and nutrient availability instead.

When You Do Not Need CO2

You can confidently skip CO2 injection if your planted tank meets these criteria:

• You are growing easy, undemanding plants: Anubias, Java fern, Bucephalandra, Cryptocoryne, Java moss, Vallisneria, Amazon sword, water wisteria, floating plants
• Your lighting is low to moderate: 20-40 PAR at substrate level, photoperiod of 6-8 hours
• You are not attempting a carpet: No Monte Carlo, no Dwarf Baby Tears (Hemianthus callitrichoides), no Glossostigma
• You accept slower growth: Low-tech plants grow steadily but noticeably slower than their CO2-supplemented counterparts
• You prefer lower maintenance: No daily CO2 monitoring, no solenoid timers, no cylinder refills

Low-tech planted tanks are genuinely beautiful. The slower growth rate is actually an advantage since you spend less time trimming and managing the tank. Many experienced aquascapers maintain low-tech tanks alongside their high-tech setups because they enjoy the simplicity.

When You Definitely Need CO2

CO2 injection becomes necessary when you want to grow plants that have high carbon demands:

• Carpeting plants: Monte Carlo, HC Cuba (Dwarf Baby Tears), Glossostigma, Micranthemum — these simply will not carpet without CO2
• Red plants: Rotala rotundifolia, Rotala H’ra, Ludwigia Super Red, Alternanthera reineckii — red colouration requires intense light, and intense light without CO2 causes algae
• Demanding stem plants: Pogostemon erectus, Rotala wallichii, Tonina fluviatilis
• High light intensity: If you are running a light above 50 PAR at substrate level, CO2 is necessary to prevent algae outbreaks. Strong light without sufficient CO2 is the number one cause of algae in planted tanks.

The critical rule is this: light and CO2 must be balanced. High light with no CO2 equals algae. Low light with no CO2 equals healthy, slow-growing easy plants. High light with CO2 equals lush, fast-growing plants of all types.

Decision Flowchart

Use this simple decision process to determine whether you need CO2:

The Liquid Carbon Middle Ground

Liquid carbon products (such as Seachem Excel, APT Fix, or Easy Carbo) offer a middle ground. They contain glutaraldehyde or similar compounds that plants can use as an alternative carbon source. They are not as effective as pressurised CO2, but they provide a measurable boost to growth and can help control certain types of algae.

Pros of Liquid Carbon

• Inexpensive (SGD 10-20 per bottle, lasts 1-3 months)
• No equipment needed beyond the bottle
• Some algae-suppressing properties
• Easy to dose (daily, measured amount)

Cons of Liquid Carbon

• Far less effective than pressurised CO2
• Toxic to certain plants (Vallisneria, some mosses can melt at full dose)
• Must be dosed daily without fail
• Does not provide enough carbon for high-demand plants
• Toxic to shrimp and fish at higher concentrations (never overdose)

Liquid carbon works best as a supplement for moderate-demand plants in a low-to-moderate light setup. It is not a replacement for pressurised CO2 in a high-tech tank.

Cost of a CO2 Setup in Singapore (SGD)

Ongoing Costs

• CO2 refill: SGD 10-20 for a 2 kg cylinder (refills at fire extinguisher shops are cheapest). A 2 kg cylinder lasts 2-4 months on a 60 cm tank at a moderate injection rate.
• Diffuser replacement: Glass diffusers become clogged and less efficient over 6-12 months. Budget SGD 10-20 annually for replacements or clean regularly with bleach solution.

For detailed CO2 system guidance, read our comprehensive aquarium CO2 guide. For a broader comparison of approaches, see our low-tech vs high-tech planted tank article.

CO2 System Components Overview

If you decide to go the pressurised CO2 route, here is what each component does:

• Cylinder: Stores liquid CO2 under pressure. Aluminium cylinders are lighter and do not rust. A 2 kg cylinder is standard for tanks up to 120 cm.
• Regulator: Reduces the high cylinder pressure to a usable working pressure. Dual-stage regulators are safer as they prevent end-of-tank dumps (sudden release of all remaining CO2 when the cylinder is nearly empty).
• Solenoid valve: An electromagnetic valve that automatically shuts off CO2 when connected to a timer. This saves CO2 and prevents excessive accumulation overnight when plants are not photosynthesising.
• Needle valve: Allows fine adjustment of the CO2 flow rate. Usually integrated into the regulator.
• Bubble counter: A small chamber that lets you visually count the rate of CO2 bubbles. Useful for consistent dosing.
• Diffuser: Breaks CO2 into fine bubbles for efficient dissolution into the water. Glass ceramic diffusers sit inside the tank; inline diffusers connect to canister filter hosing outside the tank.
• Drop checker: A visual indicator that confirms CO2 concentration in the water. Green means approximately 30 ppm (ideal), blue means too low, yellow means too high.

Singapore-Specific Factors

Singapore’s warm climate (28-32 degrees Celsius ambient) affects CO2 in two ways. Warmer water holds less dissolved CO2 than cooler water, meaning you may need a slightly higher injection rate to maintain 30 ppm compared to hobbyists in cooler countries. Additionally, higher temperatures accelerate plant metabolism, increasing carbon demand.

The good news is that CO2 cylinder refills are cheap and widely available in Singapore. Fire extinguisher servicing shops (found in industrial areas across the island) offer the most affordable refills at around SGD 10-15 for a 2 kg cylinder. Some aquarium shops also offer refill services at slightly higher prices but with the convenience of a single stop.

Frequently Asked Questions

Will CO2 harm my fish or shrimp?

At the recommended level of approximately 30 ppm, CO2 is safe for the vast majority of fish and shrimp. Problems arise only at excessive concentrations (above 40-50 ppm), which cause fish to gasp at the surface due to oxygen displacement. Using a drop checker and a solenoid timer prevents over-injection. Always run CO2 only during the photoperiod and turn it off at night.

Can I use DIY CO2 (yeast and sugar) instead of pressurised?

DIY CO2 works but has significant limitations. The output is inconsistent (high when the yeast is active, dropping as the mixture ages), it cannot be turned off at night (no solenoid), and it requires frequent re-mixing every 2-3 weeks. For a nano tank as an experiment, it is worth trying. For a serious planted tank, pressurised CO2 is far more reliable and ultimately more economical over time.

I have algae. Will adding CO2 fix it?

It depends on the cause. If algae is growing because you have strong light but insufficient CO2 (a very common imbalance), then yes, adding CO2 will help. If algae is caused by excess nutrients, poor maintenance or too long a photoperiod, CO2 alone will not solve the problem. CO2 is one part of the equation; light, nutrients and maintenance must all be balanced together.

How long should I run CO2 each day?

Run CO2 for the same duration as your photoperiod, ideally starting one hour before the lights turn on and stopping one hour before they turn off. This ensures CO2 concentration is at optimal levels throughout the entire period when plants are actively photosynthesising. A photoperiod of 6-8 hours means CO2 runs for approximately 6-8 hours as well.

Not Sure Whether You Need CO2?

The decision comes down to what you want to grow and how much maintenance you are willing to take on. At Gensou Aquascaping, we have been helping Singapore hobbyists make this decision for over 20 years. Visit us at 5 Everton Park for hands-on advice, CO2 equipment and plants suited to your goals. Contact us to discuss whether CO2 is right for your setup.

Related Reading

• What to Do After Your Aquarium Finishes Cycling
• What to Do When a Fish Dies: Removal, Testing and Next Steps
• How to Set Up a CO2 System for Beginners: Complete Walkthrough
• How to Set Up a CO2 System for Beginners: Step by Step
• Aquarium as Home Décor: Placement, Styles and Design Tips