Apart   from   the   relatively   simple   operation   of
trapping metals particles, we now have to demand that
purifiers also reduce dissolved metals. Before you can
do  that  we  are  back  to  we  ‘need  to  know’  the  total
amount of metals in the water and whether the water
is  soft  or  hard  to  determine  the  amount  of  work  a
purifier  has  to  do  i.e.  how  long  a  certain  amount  of
purification medium will be effective at protecting your
koi   and   how   often   you   will   have   to   change   the
purification medium.
       If   a   purifier   is   not   capable   of   reducing   metals,
particularly the dissolved form, metals will still end up
in the pond even though the water has been through a
purifier.   If   you   don’t   know   when   to   change   the
purification medium in a well functioning purifier for
your tap water, then you seriously risk exhausting the media  and  allowing  the  now  untrappable  metals  to
march straight through the purifier and into the pond.
       If  you  do  have  an  appropriate  purifier  and  have
worked  out  purification  medium  exhaustion  for  your
own   tap   water,   but   fail   to   change   the   purification
medium  soon  enough,  the  metals  will  again  march,
unchecked, through to the pond. Remember ‘time’ for
change  of  media  is  always  measured  in  total  metals
(etc.) and gallonage, never in weeks or months.
       You  cannot  rely  on  the  blocking  of  a  purifier  as  a
sign   that   the   filtration   media   is   now   exhausted.
Certainly  we  have  test  results  to  hand  which  show
where  both  granular  and  block  media  have  become
exhausted   even   though   no   signs   of   blocking   have
       You  might  be  doing  everything  right  but,  towards
the forecasted end of the effective life of the media, the
fish unusually flick and flash when adding new water.
This will mean that the incoming water has changed,
higher  than  anticipated  levels  of  metals  (or  another
substance)    have    entered    the    purifier,    and    the
purification  medium  is  now  exhausted  or  ineffective.
Your  koi  are  your  in-house  experts  on  water  quality.
Their flicking and flashing is telling you to throw away
the rule book and change the purification medium or
media    immediately!    If    they    continue    to    show
discomfort, seek help.
       Some  forms  of  purification  media  available  to  the
fish keeper are just totally unsuitable for koi protection,
sometimes   because   they   just   don’t   do   enough   and
sometimes because of what they actually do.
       A koi keeper gave me a purification cartridge at a
koi show which he had bought for reducing a range of
metals for his koi, the cartridge measured about 10in in
height and 2.5in in diameter. *The American cartridge
was manufactured to reduce free chlorine, entrap cysts
and  contained  a  special  medium  to  reduce  lead.  (The
only  specific  ‘metal’  reducing  medium  I  have  traced,
reduces just lead.) It is very rare to meet a lead problem
for koi in the UK, the only instances I now see tend to
be directly linked to old houses with the original lead
       Nevertheless,   the   koi   keeper   had   thought   the
cartridge  would  reduce  all  dissolved  metals  -  not  so  -
aluminium,  copper,  iron,  manganese  and  zinc  would
march   straight   through   the   cartridge   unhindered.
Where   water   needed   minor   ‘tweaking’   for   fish   the
cartridge  may  have  been  acceptable  (dependent  upon
how and where it was used) for the reduction of free
chlorine  and  perhaps  some  pesticides.  But  it  did  not
offer the fish protection the UK koi keeper sought, i.e.
the reduction of mixed, dissolved metals.
       Some  koi  keepers  seem  to  expect  that  purification
media   will   treat   more   water   than   the   main-line
purification (filtration) world know they will. The same
koi keeper thought this cartridge would not only reduce
all metals but that it would do so for many thousands
of   gallons   of   water.   *The   American   manufacturer’s
rating is for 2,000 U.S gallons i.e. only c.1,666 Imperial
(UK) gallons.
       Traditionally    for    domestic    purification    many
‘metals’ cartridges are given an effective lifetime rating
based   on   the   reduction   of   lead,   even   when   the
cartridges are capable of reducing a variety of metals.
This  is  for  two  reasons:  (1)  Lead  used  to  be  a  wider
problem  in  drinking  water  than  today.  (2)  Rating  on
lead maximises the life of a cartridge and could be seen
as a good sales gimmick as the cartridge then appears
to have a wonderfully long life.
       Let’s explore that a little further. Lead is the easiest
of  all  the  dissolved  metals  to  reduce  and  uses  the
smallest amount of purification media. As soon as there
are more metals than just lead in the water (and there
always are) the effective life of the cartridge is suddenly
radically shortened.
Example: Take a new resin cartridge (the same size as before ie. about 10in x 2.5in) for each of the following tests:
Base all tests on the use of dissolved metals. Maintain
the same flowrate in all tests.
Influent Metal Amount     Effective Cartridge Life Lead 50 ppb c.18,400 Imperial Gallons Aluminium 50 ppb c.  9,300 Imperial Gallons Aluminium 200 ppb c.  2,325 Imperial Gallons        For the treatment of water for koi we have ended-up
with   three   totally   different   effective   lives   for   one
identical   cartridge.   Forecasts   were   based   on   two
different  types,  as  well  as  two  different  amounts,  of
metals. Why those particular tests?
I 13 Based on a manufacturer’s data sheet. Based on testing undertaken at a NAMAS accredited laboratory.