U.K. which were sold to treat water for koi and to kill
blanketweed. It was identified that various purifiers
contained KDF when some koi keepers sought advice
on their koi’s health problems, varying from minor to
major. Fish keepers understand that fish health
problems are often related to more than one thing at a
time. However, even where other factors may have
been involved, general koi health improved on
cessation of using the purifiers and under taking water
changes; thus identifying the influent water treatment
as one of the potential causes of koi ill health.
Identification of the purification medium was very
simple in one instance as the particular advertising
blurb and invoice contained the name KDF! In
laymans terms what does Mr. Burrluck’s letter mean to
the koi keeper? Bi-metallic media operate by releasing
a sacrificial node. Thus the media collects some heavy
metals while releasing or ‘eluting’ other metals into
the treated water, testing of the treated water will
show the raised presence of mainly zinc but also some
copper. It is these released metals which kill not only
the bacteria but also the blanketweed.
Bi-metallic media are volatile. Different
influent waters will cause different
reactions. Therefore on some tap water
supplies smaller amounts of metals will be
released and on other tap water supplies far
larger amounts of metals will be released.
Other factors can also affect the
behaviour of bi-metallic media. E.g.
Chlorides are aggressive. Large amounts of
chlorides are present in sea water and
strong brine solutions. If these liquids were
passed through the media there is a risk of
increased metals release, plus the formation
of chlorine. This is very important to the koi
keeper who uses salt solutions as a
medication. The small amounts of chlorides
found in tap water (PCV = 400 mg/l.), or
released from brine refreshable resins such
as water softeners and nitrate reducers are
likely, at the most, to have a negligable
effect. Eg. One research programme showed
that even with chloride entering at 6,800
ppm, no free chlorine could be detected in
the effluent water.
Although Mr. Burrluck does not
currently recommend it, his letter outlines
that if bi-metallic media were to be used for
ornamental fish it should only be used in
bespoke systems. Ie. For every single
installation water should be tested before
and after the purifier to find out how many
metals are going in and how many metals
are coming out.
Once the amount of metals leaving the
bi-metallic media is known, then a resin
barrier must be properly specified to be
placed between the bi-metallic media and the
ornamental fish to soak up the released metals. This is
not only to make sure the metals are reduced to fish
safe levels but also to forecast when the resin must be
changed to ensure koi protection continues.
The letter explains that the correct resin installation
for ‘ornamental fish’ protection could impede
blanketweed control. This seems to indicate a simple
choice for the koi keeper, do we use metals in the pond
water to control blanketweed or do we reduce metals to
well published and established ‘fish’ safe levels?
Influent water changes, and this stands every
possibility of being exacerbated if the practice
continues of water being shipped around t