Seachem Flourish vs. Flourish Excel: The Confusion Explained

Because they share the same branding and sit next to each other on the shelf, thousands of beginners every year make the mistake of thinking Seachem Flourish and Seachem Excel are interchangeable.

This is a "category error." Confusing these two is like confusing a sandwich with a vitamin pill. They both help you live, but they satisfy completely different biological needs. Let's clear up the mystery of the Flourish vs. Excel debate.

1. The Nutrient vs. the Carbon

Plants are made almost entirely of carbon. They usually get this carbon from CO2 gas in the air (or injected into the water).

• Seachem Flourish contains no carbon. It contains iron, copper, manganese, and dozen other minerals. If you add Flourish to a tank with no carbon, the plants can't "process" the food and will eventually starve anyway.
• Seachem Excel is a liquid form of bio-available carbon (polyglutardialdehyde). It provides a way for plants to get carbon without a pressurized CO2 tank. It contains zero minerals. If you add Excel to a tank with no Flourish, the plant has the energy to grow but no "raw materials" (minerals) to build new leaves.

2. Excel as an Algaecide

This is the "secret" use of Excel. While Seachem doesn't market it as such, Excel acts as a mild algaecide. It is particularly effective at killing BBA (Black Beard Algae) and hair algae. If you "spot dose" Excel directly onto algae using a syringe, it will often turn red or white and die within days. Seachem Flourish does not kill algae; in fact, if you overdose Flourish in a tank with no plants, it will likely feed the algae.

3. The "Melt" Factor

Excel is a powerful chemical. Certain decorative plants, like Vallisneria, Anacharis, and Crypts, are known to be sensitive to liquid carbon. If you dose a full amount of Excel into a tank full of Vallisneria, it might "melt" away to nothing. Seachem Flourish is extremely gentle and has no such "melting" effect on plants.

4. The Algae Risk Factor

These two products sit on opposite sides of the algae war. Seachem Flourish is a potential risk; if you have too much Flourish in a tank without enough plants or CO2, you are literally feeding the algae. Seachem Excel, however, is your primary weapon. Use it as an algae-killer to "reset" the tank while Flourish provides the nutrition that allows your plants to finally out-compete the remaining algae spores.

5. Livestock & Shrimp Safety

Seachem Flourish is 100% safe for all livestock. Seachem Excel requires more caution. Because the carbon molecule is a reducing agent, it can slightly lower the dissolved oxygen levels in your tank shortly after dosing. In tanks with high fish counts or low surface agitation, it is best to dose Excel in the morning (when plants begin producing oxygen) to ensure your fish don't experience "gasping" at the surface.

6. Identifying Deficiencies

• Plants Healthy but Stagnant: If the leaves look green but the plant hasn't grown an inch in a month, you likely need the Carbon boost from Excel.
• Plants Pale or "Swiss Cheese" Looking: If the leaves are turning transparent or falling apart, you have a mineral deficit. Flourish is your solution.
• Black Beard Algae (BBA) is winning: If your plant stems are covered in dark tufts, Excel is your only liquid option to kill the algae and save the plant.

Summary: The Verdict

Choose Seachem Flourish if: Your plants are looking pale, have holes in the leaves, or simply aren't growing. This is the "food" they are likely missing.

Choose Seachem Excel if: You don't have a pressurized CO2 system and want to boost growth, or if you are fighting an algae outbreak and need a chemical tool to assist in the battle.

Written by Richard James

Aquarist, author, and creator of ShrimpKeeper.co.uk. Helping hobbyists achieve professional results through precision dosing.

View My YouTube Channel & Books →