the problem with gravel as a mechanical filter is how do you clean it?
when algae dies it just breaks down putting organic wastes back into the system. the
biofilter needs to handle the wastes, but eventually the nitrates must be dealt with.
only plants and anaerobic bacteria get rid of nitrates., plants use em to build
plant mass, anaerobic bacteria leach toxins back into the water as they get rid of
the nitrates.
when there is a big algae die off the best is to catch it in a filter and remove the
organics from the system. then let the plants in a veggie filter remove the wastes
into plant tissue that is not rotting and going back into the system. Ingrid

The gravel is the mechanical filter. One of the
whole purposes of using this kind of filter is to avoid having filter media
to clean more than once a season.


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