2 4 K  O  I     C  A  R  P W  A  T  E  R     Q  U  A  L  I  T  Y Individual metal and pesticide ‘fish safe’
values apply when that single metal (See
figure two) or sometimes a pesticide, is
on its own and all other metals and
pesticides are absent. These synergistic
effects need to be taken into account and
fish-safe values altered accordingly.      All metals inter-react with one another
and there is always more than one metal
present in the water. Together, each
individual metal becomes more of a
hazard to your koi than if it is on its own.
Therefore, for the long-term health of
your fish, it is imperative that metals are
correctly reduced.      Pesticides  react  to  one  another
differently to metals – not all pesticides
react to all other pesticides. Putting some
pesticides together causes no reaction
however, if an ‘unfriendly’ pair is put
together a reaction can occur.      Therefore when treating tap water we
have to remember that some pairs of
pesticides are fine and fish friendly but
others are fish unfriendly either singly or
in particular pairs. The more pesticides in
the water, the more likely it is that a fish
‘unfriendly’ pair may be formed. WHAT ELSE? When treating tap water for fish, we also
need to be aware of Carbonate Hardness
(KH), this is waters’ pH stabiliser. Carbonate Hardness is referred to in
drinking water reports as Total Alkalinity.
KH is often measured in German degrees
of hardness and Total Alkalinity as mg/l.         KH can be controlled fairly easily. If
your pond or tap water is below about
5.5 degrees German hardness KH (c.
100 mg/l Alkalinity), simply add a KH
buffer to the biological filters, such as
bags of loosely packed coarsely-crushed
oyster shells, ‘large’ pieces of calcified
algae or white marble chips. Be careful
not to over harden your water – aim for a
maximum KH of about 11+ German
degrees hardness (c. 200 mg/l), and test
it regularly to ensure it’s stable. If the
water becomes too hard, bypass the
buffer until the water stabilises – do not
be tempted to use water softening resins
as they are not suitable for koi ponds. WHAT CAN YOU IGNORE IN TAP
WATER FOR KOI? There are some things in tap water that
can be tolerated by koi even at its
maximum PCV, e.g. nitrate. In tap
water, the PCV limit is 50 mg/l but it is
usually far lower and can be down to as
low as <1 and <2 mg/l. Koi have shown
tolerance to over 70 mg/l although this
level is not recommended. Nitrate values
in your pond water are likely to be
different to those in the tap water as biological filters add nitrate to the pond
water (nitrate is the end product of the
nitrogen cycle). Therefore, nitrates are
best addressed once the water is in the
pond. This is just one of the reasons why
I do not recommend the use of nitrate
reducing resins with koi ponds.      Some fish keepers feel that controlling
nitrate in tap water will control blanket
weed and green water problems. This
does not take into account other factors
such as sunlight and phosphates (often
added with fish food). Practical methods
such as appropriate bacteria, calcified
algae in soft water areas (re phosphates),
shading (re sunlight) and hydroponically
grown plants in a marsh garden (for
nitrate  and  phosphates)  are  more
appropriate methods of algae control as
they are fish ‘safe’ and friendly’.      Phenols have shown a tendency to rise
in  some  koi  ponds  in  the  summer.
(Phenol is a member of a group of
substances called aromatic chemical
compounds. It is sometimes called
carbolic acid, it is derived from benzene
and can be extracted from coal tar.
Phenols are released from such things as
car tyres and garden hoses.) When
combined with chlorine TCP is formed.
So tap water has a tiny PCV limit of 0.5 µg/l all year round. Contrary to popular belief, koi keepers themselves raise phenol
values in their ponds by using old garden
hoses, which have been left full of water
or left lying in the sun. A simple remedy
is to use phenol free tubing. CONCLUSION When treating water for fish, we must put
their needs first. Only by understanding
their tolerance levels and water itself can
we hope to provide quality water for
our koi.      We must control substances, which
are harmful to fish in tap water before
they reach the fish. Care must be taken
not to add potentially harmful substances
e.g. phenols and metals. KH (Carbonate
hardness), pH, ammonia, nitrite and solid
wastes must be controlled. Aesthetic
management of water can be undertaken
within the pond e.g. green water and
blanket weed. Oxygen must be added
and new fish must be quarantined.      Fundamentally, good koi health is
established and maintained by all round
quality water and pond management. A
healthy pond should minimise the need
for medications. FIGURE THREE SUBSTANCE RENAL DIALYSIS WATER VALUE FISH SAFE WATER VALUE Total Chlorine 0.5 mg/l 0.03 mg/l Chloramine 0.1 mg/l ? 0.03 mg/l ? Copper 100 µg/l 5 - 15 µg/l “Some fish keepers feel that controlling nitrate in tap water will control blanket weed and green water problems.” A tranquil scene of swans on a reservoir
Photo: with thanks to Essex & Suffolk
Water Company Copyright, Ann Telford, AllClear Water Purifiers