Zeolite, ammonia and fish health
Zeolites are an ideal means of managing ammonia levels in the
short-term until full filter active is restored or achieved. Even
modest levels of ammonia are a threat to fish health. This is
particularly a problem in new ponds and aquaria where we have to let
ammonia levels rise a little to encourage the establishment of
nitrifying bacteria in the filter. Elevated ammonia can occasionally be
a problem in established set-ups.
What are zeolites?
These are naturally occurring types of minerals, although because of
their usefulness as molecular sieves they can now be artificially
produced. In their natural form they are aluminosilicates, which are
normal silicate minerals containing aluminium. The structure is such
that these minerals can loosely bind positive charged ions, usually
They act as ion-exchangers and 'swap' their sodium ions, for other
positively charged ions, for example calcium or ammonium. So they are
often used for water softening to remove hardness-forming calcium ions.
Fish keepers can make use of this unusual characteristic and employ them
to remove ammonia (or more strictly ammonium - NH4+) from the water.
The required amount is simply placed in the filter just before
the water is returned to the pond or tank. Don't place it before the
biological section otherwise there may not be enough ammonia left to
encourage the growth of nitrifying bacteria.
Depending on the current ammonia levels, the zeolite is removed when
it is 'full' and left overnight to soak in a very strong salt solution,
during which the collected ammonium is "swapped" for sodium
(you will recall that salt is actually sodium chloride). After a good
rinse in clean water it is ready for use again
How much and how often?
For aquaria use, zeolite and other
ion-exchanger products usually come in pre-prepared pouches with
instructions. For pond use it is best to have at least two 10 kg
sacks - one in use, the other being recharged.
Initially it will probably need to be
changed daily, until such times that ammonia test kit readings
show that levels are stabilising. Once this happens the
period between cleans can be extended
To clean it use 2-3 oz salt per
gallon of water. The actual amount is not critical as long as it
is good and salty.
It should only be used to manage an
existing problem and not used on a long-term 'just in case' basis.
First, if used permanently there is always the risk that it will
'dump' its ammonium collection. Secondly, it also acts as a
water-softener and will remove calcium from the water.
Initially, even with zeolite it may still
be necessary to do partial water changes to keep ammonia at an
Zeolite cannot be used in ponds or
aquaria where the water is salted