CO2 Addition Guide for Planted Tanks

CO2 Supplementation Guide for Aquatic Plant Tanks | Necessity, Equipment Selection, and Dosage Determination

For those who want to grow aquatic plants more beautifully and vigorously, CO2 supplementation is an indispensable technique. Aquatic plants grow through photosynthesis, and this process requires carbon dioxide (CO2). The CO2 dissolved in tap water is often insufficient, and by supplementing CO2, aquatic plant growth improves dramatically. This article explains the basics of CO2 supplementation through equipment selection in detail.

Why CO2 Supplementation Is Necessary

Aquatic plant photosynthesis is the reaction "light + CO2 + water → sugars + oxygen." Even if you ensure sufficient light, photosynthesis becomes limited when CO2 is insufficient.

When CO2 is insufficient: - Growth slows or stops - Leaves become small and thin - Plants are easily deprived of nutrients by algae - Red aquatic plants lose their vibrant coloration

Conversely, when CO2 is supplemented properly: - Abundant oxygen bubbles emerge from aquatic plants (pearl glossing) - Growth accelerates and leaves become large and beautiful - Algae growth is suppressed

Aquatic Plants That Benefit Most from CO2 Supplementation

Plant species that strongly benefit from CO2: - Foreground plants like hair grass and glossostigma - Rotala species (various types) - Nymphaea species (emersed forms) - Hydrocotyle species (various types)

Species that grow easily without CO2 (suitable for low light and no CO2): - Anubias species - Cryptocoryne species - Microsorum - Moss species (such as willow moss)

Methods of CO2 Supplementation

Fermentation-Based CO2

A method where sugar, yeast, and water are mixed to naturally ferment and generate CO2 that is added to the tank.

Advantages - Inexpensive materials (a few hundred yen per month) - Low initial investment

Disadvantages - Unstable CO2 generation (dependent on temperature) - Regular refill needed (every 2-4 weeks) - Fermentation continues at night, making it difficult to switch between aeration and CO2 supplementation

Suitable for: 30-60cm tanks, beginners, low budget

Cylinder-Based CO2 (Small Cylinders)

A method using commercially available small CO2 cylinders (disposable type).

Advantages - Stable CO2 supply - Less labor-intensive than fermentation method

Disadvantages - Recurring cost of cylinders (approximately 500-1500 yen per month) - Timer management required

Suitable for: 30-90cm tanks, intermediate users

Cylinder-Based CO2 (Large Cylinders / Commercial)

A full-scale system connecting a regulator to large CO2 cylinders (5kg or 10kg).

Advantages - Lowest running costs - Stable long-term supply

Disadvantages - High initial investment (regulators, solenoid valves, etc.) - Large cylinder size

Suitable for: Large tanks 90cm or larger, advanced users

Required Equipment

CO2 Diffuser A device that breaks CO2 into fine bubbles to dissolve it in the water. Available in glass airstone type or inline type (connected to filter piping).

Bubble Counter A device to check the CO2 dosage (how many bubbles per second). Essential for stable dosage management.

Solenoid Valve When combined with a timer, automatically controls CO2 on/off in sync with lighting. Prevents oxygen depletion at night from excess CO2.

CO2 Timer A timer that turns CO2 supplementation on and off at the same timing as lighting. The typical setting is to turn CO2 on 30 minutes before lighting turns on and off 30 minutes before lighting turns off.

CO2 Dosage Guidelines

The standard dosage guideline is "1-3 bubbles per second." The precise amount can be calculated from the relationship between pH and carbonate hardness (KH).

Simple Judgment Criteria Whether bubbles are emerging from aquatic plants is the most straightforward indicator. The ideal dosage is slightly higher than the amount at which bubbles first appear.

Verification Through pH Change CO2 increase lowers the water's pH. By measuring pH before and after CO2 supplementation, a decrease of 0.3-1 is an appropriate guideline.

CO2 Test Solution (Drop Checker) A convenient tool using specialized test solution to confirm the current CO2 concentration by color. Green indicates appropriate level (20-30ppm), blue indicates insufficiency, and yellow indicates excess.

Precautions for CO2 Supplementation

Stop at Night It is important to stop CO2 supplementation at night (when lighting is off). Adding CO2 during hours when photosynthesis is not occurring risks oxygen depletion and fish suffocation.

Unnecessary for Fish-Only Tanks CO2 supplementation provides no benefit to fish-only tanks and actually carries an oxygen depletion risk.

Summary

CO2 supplementation is an effective method to elevate aquatic plant tank management to the next level. First, try the fermentation method and experience your aquatic plants growing healthily. Once you see improvements in growth and beauty, consider upgrading to cylinder-based CO2 supplementation.