I have used AFM (Active ...

I have used AFM (Active Filtration Media) successfully for the last 15 years.  However, if the particle size in the water feeding the plant is too large or levels are too high then the filters will need backwashing more frequently.  A plant using AFM still has had the same backwash rate over the 15 years without any deterioration in water quality.  AFM doesn't become colonised by bacteria and the particles have a smoother surface making better filtration.  They like other filtration methods don't like algal strands, which can cause problems.