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Ovviamente tutte le spugne vanno sciacquate nell'acqua prelevata dall'acquario comunque per gli intervalli di sostituzione sia il manuale uso e manutenzione sia il sito dicono cosi:

Care and maintenance of the JUWEL Filter System
Maintenance of the Filter System
The JUWEL Filter System requires very little maintenance if you follow the following
instructions.
- Replace the white filter wool pad once a week. If you have large fish, then this may
require changing slightly more frequently. This will ensure that the filter sponges will
not be clogged by larger dirt particles.
- Replace the black activated carbon sponge every 4-6 weeks. Again, if you have large
fish then this may be to be more frequent. This ensures that any chemical impurities
from the water will be removed. Please note that the chemicals which are absorbed by
the activated carbon contained in the sponge, will be released to the water again if
the change intervals are too long.
- If the filter wool and the activated carbon sponge are replaced as suggested, then it
is sufficient to carefully clean or replace the coarse blue sponges at 6 weeks and
the fine blue sponges at 3-6 months only.
Important - Cleaning or replacing the blue filter sponges will affect the bacteria
cultures. We recommend therefore, that only one of the sponges at a time is cleaned or
replaced, never at the same time.
You do not need to worry about the liquid dirt accumulating at the bottom of the
filter housing. Normally, this dirt contains important biological substances which
enhance the water quality.
Please do not worry if some dirt gets into the water during the cleaning process
causing cloudiness. After the filter system is back in operation, the water will soon
clear again.
- In order to allow a proper level of micro-organisms in the filtration system it is
recommended to exchange the sponge every 6 weeks. The nitrate removal sponge
contains bacteria, which will after a while reduce the nitrate level in the aquarium
significantly.