Remains in water longer than free chlorine. Therefore
potentially carries greater risk of damaging fish gills.
Synergistic effects (see previous article in September
2000 issue of Koi Carp). Can damage gills, liver,
kidney and central nervous system. Can cause poor
growth and spinal deformities.
In hard water, iron oxides can coat fish gills and
interfere with oxygen transfer across gill membranes.
1) Attack gills, liver and kidneys.
2) Can interfere with the development of red blood
corpuscles in the lining of the koi’s head and their
kidney. Can cause anaemia which (a) can cause
difficulty in transferring oxygen around the body and
(b) lead to a lowered immune system.
3) Because of (2), koi are more open to bacterial,
fungal and parasitic invasion.
4) Can attack the reproductive organs.
5) Weakens skin and scale causing wound-healing
difficulty, which can lead to ulceration.
Careful purifier choice is needed to prevent the health problems listed in Figure 2. Correct water management can reduce the need for expensive medications and make your’s and your kois’ lives less stressful. Free Chlorine Short-term disinfectant. Fairly easily gassed off.            Chloramine Long-staying disinfectant. In my view, the hardest           
substance to reduce when treating tap water for koi.      
Pesticide Group Huge generic group including algicides, fungicides,
herbicides, insecticdes and molluscicides.
Toxic Metals Particles of toxic metals. i.e. metal oxides
hydroxides and carbonates.
Toxic Metals Dissolved Metals. Generally speaking, more
damaging to koi than metal oxides. Have synergistic
effects (see pesticides). In my view the least
recognised and most damaging group of
substances in tap water to koi
               urifiers are used to improve koi
               health. It is important not to
forget they are just one item in a
cycle of events, which govern good koi
health. Therefore, when running a koi
pond all the parameters in Figure 1 need
to be ‘sorted’.  
     Tap   water   in   the   UK   varies
enormously; some waters need tiny
tweaking  while  others  need  radical
intervention. Correct tap water treatment
will help ‘improve’ your koi.  Perhaps their
colours are a little faded, they are slightly
listless, they don’t feed enthusiastically or
they frequently flick and flash. As we go
up the scale of health problems related to
tap water the symptoms escalate. See
Figure 2.
TESTING AND VALIDATION There are no  professional
organisational badges or logos, which
identify the suitability of purifiers for
fish protection.  
     The  UK  Water  Research  Centre
(WRc) tests non-metallic products using
BS6920 protocols related to domestic use
i.e. human consumption. These protocols
are not related to fish. The WRc have
stated they do not test products for-
     In the USA, industry standard testing
follows NSF protocols to meet FDA
requirements. Once again related to
human consumption and not fish use.
     OATA (formerly OFI) worked with
the  aquarium  industry  to  establish
standards for building aquarium, they do
not test or validate ‘fish’ purifiers. Fish
related testing of purifiers is outside the
professional remit of these and other
organisations. You need some basic
knowledge of purifiers and testing criteria
to make the right choices. Some purifier
parts can be chosen fairly easily:
VESSELS: These are the outside ‘bits’ which hold the cartridges. There are
relatively  few  vessel  manufacturers
throughout the world and vessels look
fairly similar. There are differences, see
Figure 3. Having chosen the ‘outside’ part
of the purifier, choose the ‘insides’ with
even greater care. Pre-filters come first.
PRE-FILTERS: (See Fig 4, p15) Pre- filters are sieves designed to trap particles
in tap water to protect purification
Ann Telford gives us some points to consider... CHOOSING A PURIFIER P
For background reading refer to Ann’s articles in the September and October issues of Koi Carp
Pond Management Good koi health relies on good pond management Change tap water from
being water designed for
people to water designed
for fish before it reaches
your koi.
Do not
tock the
pond or o
feed the fish
Ensure koi
‘safe’ materials
are used to
construct the
Oxygenate pond water
and filter
Keep filters and bottom
drains clean
Quarantine new fish Buffer soft water (KH) Control pH, ammonia, nitrate & solid waste