Biological filtration is the process by which waste products,
principally ammonia, in ponds and aquaria are broken down
by bacteria.
The bacteria which are responsible for nitrification require:
- a surface on which to grow (the larger the surface area,
the greater the population which may grow)
- a good supply of dissolved oxygen
N.B. an active filter may use more oxygen that the livestock
in the water it processes
- a supply of nutrients; ammonia and nitrites
The bacteria responsible for denitrification require:
- a surface on which to grow
- a supply of nutrients
- principally nitrates
- secondarily
- if methanol or a similar chemical is present,
nitrogen gas will be formed
- if other organic materials are present ammonia
may be formed
Oxygen kills the bacteria responsible for this process.
A filter may be said to be mature when any ammonia entering
a tank is instantaneously converted to nitrite and then in
turn to nitrate.
Biological filters are only mature for specific conditions.
If the stocking density or feeding increases then the filter
needs a further period of maturation.
