People  can  tolerate  less  bacteria  and  more  metals
than fish while fish can tolerate less metals and more
bacteria than people. A nice neat little transposition!
Domestic purifying cartridges are sometimes therefore
impregnated  with  metals  to  kill  bacteria  for  ‘people’
protection. Metals are released into the treated water,
suddenly these domestic cartridges stop being a people
protector and become a potential fish damager. These
cartridges are not suitable for the treatment of water
for koi or any other fish.       Bi-metallic media are also ‘bacteria killers’ used in
water   treatment   systems   for   ‘human’   use.   Indeed
experiments were conducted in the USA on the use of
a   bi-metallic   medium   (KDF)   which   demonstrated
(among  other  things)  its  reduction  performance  of
Enterobacter and other endogenous bacteria present in
influent   water.   This   bactericidal   effect   led   to   the
conclusion  that  the  device  “...may  be  useful  in  the
control   of   potentially   harmful   bacteria   that   may
inadvertently enter potable water supplies.”       It is reported separately that short-term tests were
undertaken on expendable fish which were purportedly
less sensitive than koi, on the use of bi-metallic media
as a medication (bacteriocide). The experiments were
reported  to  be  successful,  however  these  tests  and
results  are  ‘word  of  mouth’  and  I  have  no  factual,
controlled, experimental data to hand to support these
claims.  As  with  all  medications,  whereas  controlled,
short-term  amounts  can  be  successful  if  used  for  the
correct  species  of  fish  and  health  indications  etc,  the
same  medication  can  be  harmful  to  different  fish,  or
can  be  harmful  to  the  same  fish  either  in  different
concentrations or over longer periods of contact time.
Later, I will show that for the treatment of koi pond
water, the indiscriminate use of bi-metallic media can
be harmful to koi.       As  these  last  few  and  the  following  paragraphs
illustrate,   claims   of   bacteria   control   are   a   useful
indication  that  a  water  purifier  adds  metals  to  the
treated water.       What are bi-metallic media? They are a mixture of
tiny  metal  granules  which  look  like  splinters.  Some
granules are pure copper and the others are pure zinc.
There are three main types of bi-metallic media; fine
granules which are impregnated in filter pads for coffee
machines   etc.,   larger   granules   which   are   used   in
standard  water  treatments  and  finely  knitted  ‘wools’
which  are  used  in  water  recirculation  systems  eg.
water towers. Initially the granules are the goldy and
browny colours we would expect but they oxidise and
turn black.       The  original  bi-metallic  medium  was  invented  in
America and was patented. It was named KDF. It is a
superb  product  when  used  correctly  for  the  correct
filtration purposes. Seductively, it also has a side effect of killing algae which is very tempting to the fishkeeper
- here I am specifically thinking of the control of green
water   and   blanket   weed.   Unfortunately   bi-metallic
media are unsuitable, as are all metal based ‘bacterial
killers’, for the treatment of water for ornamental fish
in standard (off-the-shelf) purification systems.       Many professionals in the water industry take great
care that the ‘right’ type of filtration media is used for
the  ‘right’  purpose:  Mr.  Burrluck  is  a  director  of  a
company  who  are  the  European  Distributors  of  KDF
granules.  He  wrote  a  letter  which  was  published  in
Aquarist    and    Pondkeeper    in    November    1996^¤.
Although   his   following   letter   is   technical,   it   is
important reading. K O I 15 Dear Sir,       With reference to your article ‘Fishkeeping’s Hidden Agendas’
(A&P, August) and in particular references to the use of bi-metallic
media to remove or regress undesirable elements, as a supplier of
such media I would like to offer my comments for your review.       My job function brings me into contact with a whole host of
water treatment applications and the relevant solutions for industrial,
commercial and domestic situations are wide ranging. One type of
treatment we currently market and distribute is a redox alloy media.       Before offering the use of this process media to an end user, a
certain amount of accurate information and integrity must be gathered
to assist in planning of water treatment systems for its use in cooling
towers and other recirculatory systems, drinking water improvement,
dechlorination, iron, H2S and heavy metal reduction and control of
bacteria, algae and hard scale.       When considering the use of the process media it is important
to understand that the media works through REDOX principle (gaining
and losing of electrons). Depending upon certain applications this
principle could lead to the re-deposit of ionic metals, through the redox
alloy media’s slight elution (release) of copper and zinc. In many
applications that are commercial, industrial or domestic, the elution
has no consequence to the system or the vast majority of people
involved, however, it could possibly be detrimental to ornamental fish if
there is no additional finite removal of these ionic metals down to the
considered fish safe levels required.       As a supplier of water treatment equipment and packages we
have a responsibility to ensure that end user requirements are met and
that satisfactory water treatment is achieved. Water supply quality is
sometimes erratic and far greater accuracy for removal of resident
‘contaminants’ is required for ornamental fish than in many other water
treatment areas.       Although field and lab testing results are available for the use of
our process media, when comparing the measured quantities of
redeposited copper and zinc from redox alloy media against published
and accepted fish safe levels we feel, at this time, that the promotion of
our process media into the ornamental fish keeping market as a
feasible integral component of standardised water filtration systems is
not a responsible act without first establishing set parameters.       It may be possible to offer the use of our process media as part
of a combination filtration stage whereby adequate control and contact
time for the treatment to take place is achieved. Stage treatment would
necessarily include the use of finite or corrective and supplementary
medias to remove eluted ionic metals from the treated water. Due to
inherent complexities of using redox alloy media this would be brought
about by exhaustive testing and on-site trials of managed systems in
order to determine filtration stage design for individual applications for
the achievement of identifiable certification. By undertaking corrective
measures to remove ionic metal elutions on the treated water, redox
alloy media function for bacteria and algae control could be impeded.       I hope that this information will be of benefit to your readers in
that it clarifies our position in the market and the possible concerns of
installing systems that incorporate bi-metallic media using the redox
principle.
S. D. Burrluck,
Uni-Flo Services Ltd,
Brough, E. Yorks HU15 1YQ ¤ Copyright approval previously obtained from Mr Burrluck.