Seachem Flourish Excel is a bioavailable organic carbon supplement for freshwater planted aquariums. It provides aquatic plants with an accessible carbon source that can be used alongside — or instead of — CO₂ injection, supporting healthy plant growth across a range of tank setups. Available in 100ml, 250ml, and 500ml sizes.

Flourish Excel delivers carbon in a form that plants can absorb directly at the cellular level, bypassing the need for dissolved CO₂ as an intermediary. It contains polycycloglutaracetal compounds that act as photosynthetic intermediates in the carbon cycle. Regular dosing promotes vigorous leaf growth and can help suppress algae by giving established plants a competitive edge. Compatible with CO₂ systems — it supplements rather than replaces pressurised injection.

Planted tank enthusiasts reach for Flourish Excel when CO₂ systems aren't practical — particularly in smaller tanks or low-light setups where pressurised CO₂ is a disproportionate investment. It's also used by aquarists managing algae, where consistent carbon availability helps established plants outcompete new growth.