Last  month’s  section  left  a  cliff  hanger  -  that
Purifiers  can  be  responsible  for  metals  in  pond
water at above safe levels for koi. How can that be?
T            HE HOUSING of a purifier must be checked if it
           is made of metal. Does the metal container leach
(release) metals into the water? What about the
solder used for the metal seams? Housings and solder
which  are  perfectly  acceptable  for  ‘domestic’  water
treatment aren’t necessarily suitable for ‘fish’ use.
       Having  checked  the  ‘outsides’  of  the  purifier  we
then  need  to  move  onto  a  purifier’s  ‘innards’.  The
simplest way purifiers can let metals through, is that
the  problem  hasn’t  been  correctly  identified  and  the
wrong purifier has been used. Some purification media
just  do  not  reduce  metals  or  do  not  reduce  dissolved
metals.    Examples:    Activated    carbons    are    not
manufactured  to  reduce  dissolved  metals.  Activated
carbon   blocks   or   a   fine   pre-filter   can   trap   metal
particles,   from   that   angle   one   could   claim   that   a
purifier reduces heavy metals. But it’s not quite that
simple for koi protection. Before we go any further it is
important to discuss the main forms of metals as they
are  found  in  tap  water.  All  metals  are  divided  into
various groups in water. The main groups are:
     (1)    Particles    of    metals    which    are        called
particulates.   These   particles   can   be   suspended   in
water. It’s a bit like one of those medicines for stomach
upsets. In the bottle you can see a sludge at the bottom
while  the  upper  liquid  is  clear.  Before  taking  the
medicine  you  shake  the  bottle  so  that  the  sludge
(particles)  gets  mixed  up  with  the  clear  liquid,  the
whole bottle of liquid turns opaque and gains a uniform
colour. This is called a suspension. The particles don’t
dissolve into the liquid and when the bottle is left to
stand  the  particles  separate  back  out  to  reform  the
sludgy stuff at the bottom of the bottle. Apart from the
risk of iron particles coating gill plates and interfering
with oxygen transfer across the gill membranes, metal
‘particles’  are  the  least  damaging  form  of  metals  for
     (2) Other metals are in dissolved form. These are
the metals most likely to cause damage to our koi. They
do  not  register  on  standard  fish  test  kits,  cannot  be
seen  and  can  only  be  traced  by  water  reports  or
additional laboratory testing.
      The   split   between   the   mix   of   particulate   and
dissolved metals varies according to the type of water.
Unfortunately this is where rule-of-thumb comes into
play as laboratories reduce all metals to dissolved form
for  testing  purposes  and  do  not  normally  report  any
split between dissolved and particulate metals in the water  they  tested.  Generally  speaking,  in  soft water approximately two thirds of the metals are in dissolved form and one third are in particulate form. In hard water the mix is reversed  so  now  about  one  third  of  the metals  are  in  dissolved  form  and  two thirds  of  the  metals  are  in  particulate  form.  As  dissolved  metals  are  more
 damaging   I’m   afraid   that,   again
 generalising,  koi  keepers  may  face  a
 bigger   problem   in   soft   water   areas
 than koi keepers in hard water areas.
 But  before  ‘hard  water’  koi  keepers
get unbearably smug, please remember
 that we are in a hard water area and we
lost most of our koi collection because of
metals damage. Part 2 By  Ann Telford THE UNDER COVER STORY OF WATER PURIFIERS & Koi I 12            Some of these Koi unfortunately were
lost due to high levels of metals in the pond water
Photograph courtesy of Brian Batty.