Seachem Excel is not a carbon source, it is not CO2
and it is not a CO2
replacement. Aquarium product manufactures are masters at marketing, and mislead the buyer with many products.
Excel is a mild algaecide that allows users to run slightly higher light with a reduced risk of an algae outbreak. It may or may not help break down protein films growing on plant tissue, allowing plants better access to atmospheric CO2
naturally occurring in the water.
Excel can be used to spot treat, and create plant dips to help control algae.
Excel should be used as an algaecide, not a carbon or CO2
source / supplement.