Will activated Carbon affect fertilizer usage?Updated a month ago

Activated carbon is effective at removing larger organic molecules and less effective at remove simple dissolved ions. Here is a table that gives you a good idea of what is removed by carbon.

High to moderate adsorption of:
Arsenic, Bleach, Chlorine, Colors, Dyes, Hydrogen Peroxide, Insecticides, Monochloramine, Odors (usually larger organic molecules), Detergents, Dissolved Organic Compounds (DOC), Hydrogen Sulfide, Mercury, Soap, Solvent

Fair adsorption of:
Complexed trace elements (due to organic chelator), Iron(as FE 3+), Lead, Vanadium.

Low to no adsorption of:
Alkalinity, Ammonia, Carbon Dioxide, Nitrates, Phosphates, Potassium 

Activated Carbon can have some impact on removing chelated Iron/trace elements from liquid fertilizer, however, the impact is low enough to be not a concern for most tanks. There is usually enough dwell time in the water column for plants to grab a fair portion of those nutrients before activated carbon strips it from the water column.

Activated Carbon will have no impact on macro-nutrients.