What is Seachem Flourish Excel?
Seachem Flourish Excel is a liquid carbon supplement designed for planted aquariums. While not true gaseous CO₂, it provides plants with a usable form of organic carbon (glutaraldehyde-based compounds) that they can metabolize for growth.
It is commonly used in:
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Low-tech aquariums (without pressurized CO₂ systems).
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Smaller tanks where pressurized systems may not be practical.
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Algae control, as Excel can suppress certain algae species (especially black beard algae).
How Liquid CO₂ Differs from Pressurized CO₂
| Aspect | Liquid CO₂ (Excel) | Pressurized CO₂ Injection |
|---|---|---|
| Form of Carbon | Provides organic carbon (not actual CO₂ gas). | Supplies true CO₂ gas, dissolved directly in water. |
| Efficiency | Supports plant growth but less efficient than gas. | Most effective method for fast growth and demanding plants. |
| Scalability | Best for nano to medium aquariums. | Works for tanks of all sizes, especially large aquascapes. |
| Algae Impact | Can suppress some algae. | Doesn’t directly fight algae but prevents it via strong plant growth. |
| Cost | Lower upfront, regular purchase needed. | Higher upfront cost (regulator, cylinder, diffuser), but cheaper long term. |
| Control | Limited — dosing is fixed. | High precision: bubble counters, pH monitoring, solenoids. |
Key Limitation: Liquid CO₂ cannot reach the same saturation or consistency as pressurized injection. For high-light, demanding aquascapes (e.g., carpeting plants, red stems, SPS-like growth), pressurized CO₂ is the only reliable option.
How to Dose Seachem Excel
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Initial dose:
5 mL for every 40 L (10 US gallons) after a large water change. -
Daily maintenance dose:
5 mL for every 200 L (50 US gallons). Smaller tanks should be adjusted proportionally (e.g., 1 mL per 40 L). -
Application tips:
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Dose once a day, preferably after lights turn on.
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Direct spot-dosing onto algae patches (with a syringe) can be effective against black beard algae.
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Avoid overdosing — plants benefit only up to a point; beyond that, livestock may be harmed.
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⚠️ Safety and Handling Precautions
Seachem Excel contains glutaraldehyde derivatives, which can be harmful if mishandled.
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Do not overdose: Excess can burn plant leaves and stress fish/shrimp. Sensitive species (e.g., Vallisneria, mosses, ferns) may “melt” if overdosed.
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Handle with care: Avoid skin and eye contact; wash hands after use.
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Store safely: Keep out of reach of children and pets.
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Avoid mixing directly with livestock when spot-dosing; use a syringe carefully.
When to Choose Liquid CO₂
Liquid CO₂ is ideal if:
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You keep low to medium light tanks with hardy plants (Anubias, Java Fern, Cryptocoryne, stem plants).
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You want a simple, low-maintenance solution without extra equipment.
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You want an algae management aid in addition to nutrients.
Choose pressurized CO₂ if:
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You keep high-light setups with carpeting or red plants.
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You want fast, lush plant growth.
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You run tanks larger than 100L, where liquid CO₂ becomes impractical and costly.
Final Word
Seachem Flourish Excel is a fantastic tool for low-tech planted tanks, offering both a source of organic carbon and an added algae-fighting benefit. However, it’s not a substitute for a full pressurized CO₂ injection system, especially for aquarists aiming at high-demand aquascapes. Used correctly and safely, it can make planted aquariums healthier, greener, and easier to manage.