Think  of  a  bottle  of  medicine  for
upset  stomachs.  Standing  in  the
cupboard the medicine divides out into
a  clear  coloured  liquid  at  the  top  and
opaque  ‘sludgy’  stuff  at  the  bottom  of
the  bottle.  The  sludgy  stuff  consists  of
undissolved  particles.  Shake  the  bottle
thoroughly and the two things combine
to form an opaque mixture through the
whole of the bottle. The ‘sludge’ hasn’t
dissolved, it has mixed in with the clear
liquid  to  form  a  ‘suspension’.  The
‘sludge’  is  the  equivalent  of  metals
particles  in  water,  i.e.  the  part  of  the
metal in suspension.  
     For  a  clear  liquid  to  be  coloured
but  to  remain  clear,  something  has
been  dissolved  in  it.  These  dissolved
substances,  are  now  called  a  solution.
This  is  similar  to  the  second  form  of  a
metal found in water, the dissolved part.
Apart  from  iron  particles  coating  fish
gills  in  hard  water,  it  is  the  ‘dissolved’
metal,  i.e.  the  part  of  the  metal  in
solution, which is more harmful to koi.  
     The amount of each metal in particle
or  dissolved  form  varies  depending
upon the type of water the metal is in.
See Figure One above.
     So there are two forms of each heavy
metal in the water, they each need to be
‘reduced’ differently.
Pre-filters, Carbon and Ceramic Blocks:
PROS:  They  trap  ‘particles’  of  metals,
sand etc. Linking this with Figure One,
if  tested  on  hard  water,  an  activated
carbon block or pre-filter could be rated
to  reduce  about  60%  of  heavy  metals.
The only heavy metals this rating applies
to,  is  the  reduction  of  particles  of
metals,  i.e.  the  undissolved  metals,
which  are  sometimes  referred  to  as  a
suspended metal.
CONS:  They  do  not  reduce  dissolved metals. Activated Carbons (block or granular):
PROS:  They  are  cheap  and  readily
available.   They   reduce   chlorines
and pesticides.
CONS:  They  do  not  reduce  dissolved metals. In the filtration (purification)   industry  it  is  accepted  that  if  an
  activated  carbon  temporarily
collects  a  dissolved  metal  such  as
zinc,  it  then  ‘dumps’  it  back  into
the treated water. NOTE:  Some  activated  carbon  block cartridges  are  mixed  with  an  extra
substance  to  reduce  dissolved  lead.
However,  apart  from  a  house  with  old
lead plumbing, lead in UK tap water is
now so low that lead on its own is not
generally a problem for UK koi.
Ion-Exchange Resins: The dissolved form of metals in general
can be a problem for koi health, either
in  a  minor  or  a  major  way.  It  all
depends  upon  the  quantity  of  a  single
metal  or  the  total  metals  in  individual
tap waters.  
     The  fish  world  mainly  relies  on  ion
exchange  resins  to  reduce  dissolved
metals.  These  resins  exchange  one  ion
for  another.  It  is  a  bit  like  throwing  a
pink  jumper  out  of  a  drawer  to  make
room  for  a  blue  one.  Different  resins
reduce  different  substances  e.g.  metals,
nitrate or some soften water.  
PROS:  Reducing  dissolved  metals  can be very beneficial to koi. CONS:  Great  care  has  to  be  taken choosing  resins.  Some  resins  ‘throw
away’  substances  which  are  actively
dangerous to koi, e.g. acids.  
     Any  brine  refreshable  resin  throws
away a salt-based substance as it softens
water or collects nitrates – this is usually
Sodium  Chloride.  There  is  a  potential
risk  that  the  discarded  substance  could
react with some medications such as the
Formaldehyde  part  of  Formalin  and
Potassium  Permanganate.  Koi  cannot
tolerate  uncontrolled  amounts  of
Chlorides.  They  should  not  be  kept
permanently  in  a  ‘brine’,  that  is  a
‘salt’ solution.
     Brine  refreshable  water  softening
resins are not allowed to be installed on
drinking  water  systems  for  us  and
should be seen as unsuitable for koi.
The  right  purifier  has  to  be  chosen  to
protect koi.
Domestic Purifiers
PROS: They treat water in the home so
it is pleasant for ‘people’ to drink. They
tend  to  change  the  smell,  colour  and
taste  of  water,  sometimes  they  soften
water as well.
CONS:  Domestic  purifiers  can  contain 1 8 K  O  I     C  A  R  P A  N  N     T  E  L  F  O  R  D FIGURE ONE WATER TYPE AMOUNT OF METALS IN PARTICLE FORM (SUSPENSION) AMOUNT OF METALS IN DISSOLVED FORM (SOLUTION) Hard Water About two thirds About  one third Water that is neither About 50% About 50% soft nor hard Soft Water About one third About two thirds Many things can contribute to koi ill
health and death. Mr Brian Batty lost 47
koi. At that time he used zinc and copper
to control the blanketweed. Mr Batty had
the courage to build another koi pond
and now controls the blanketweed in a
different way. Today he has a pond of
healthy koi which he can enjoy.
CASE STUDY TWO Photos supplied Brian Batty