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Malachite green and formalin treatments
Malachite Green and Formalin are one of the main cornerstones of fish
disease treatments having been used for many years against a range of
parasites. They can be used together or separately as anti-parasite
treatments against as Gyrodactylus (skin flukes), Dactylogyrus
(gill flukes), Ichthyobodo (Costia), Trichodina , Chilodonella
and Ichthyophthirius (white spot).
The dynamic duo of MG&F is the treatment of choice against white
spot (Ich). The relatively long active life of this treatment, together
with the low filter toxicity makes it ideal for tackling the complex
life cycle of this protozoan parasite. It also has a high success rate
with Costia and Chilodonella and would, in most
circumstances be my first choice. I have found a mixed result with Trichodina
and flukes sometimes a total success, but in other cases not so good. It
seems likely that the stronger dosage is needed against these two
parasites and a follow up examination to assess the success of the
treatment.
Malachite green has powerful anti-fungal properties and is used
against Saprolegnia (fungus) either when present on fish or to as
a prophylactic treatment to protect fish-eggs from infection. It is
important to realise that in most cases, fungal infections of fish are
secondary infections and unless the primary infection - quite often
bacterial - is resolved then anti-fungal treatments such as malachite
are unlikely to be successful.
Malachite green and formalin are toxic poisons
Malachite green acts as a respiratory poison, damaging the cell’s
ability produce energy to drive vital metabolic processes. Formalin is a
powerful disinfectant used to kill microorganisms or as a preservative
for biological specimens. It works by reacting with cell proteins and
nucleic acids - altering both structure and function. These chemicals
can be used separately but are usually used together because they exert
a synergistic effect; that is, together they give a greater effect than
the sum of their separate individual capabilities.
They exert a mild anti-bacterial effect and in most circumstances
will not destroy biological filtration bacteria, although they may ‘knock
the filter back’ for a short while. However, it is still advisable to
turn off or by-pass the filter system for a few hours if possible and as
with any treatment always turn off any UV lamps. When using to treat
against Ichthyophthirius (white spot or Ich) then it is important
to keep the system running in order to destroy all stages of the
parasite’s life cycle.
During prolonged treatments, especially when the filter has not been
isolated, it is important to test for ammonia and nitrite on a daily
basis in case the filter has been affected.
Using malachite green and formalin
As you might expect both of these chemicals are affected by
variations in water chemistry. Both can be ‘bound out’ of the system
by high dissolved and particulate organics such as fish waste, detritus
and algae. Formalin is more toxic in soft, acidic water and also removes
oxygen from water so vigorous aeration most be applied. Each 5mg
of formalin removes 1 mg of dissolved oxygen from the water. Malachite
green is also more toxic at low pH as well as high temperatures.
Malachite green has two forms depending on pH. The initial strong
green coloured for prevails at low pH (acidic), while in alkaline water
it is converted to a colourless carbinol form. So in alkaline water it
may seem that it has disappeared, but it is still present, but
invisible!
More on malachite green and formalin:
Wear gloves and goggles when handling malachite green or
formalin. Do not inhale the fumes of formalin and always handle in
a well-ventilated area. Both are potentially dangerous. Malachite
is a respiratory poison as well as being a suspected carcinogen.
Malachite green penetrates deeply into fish body tissues and
may have a use against Proliferative Kidney Disease (PKD) in
salmonids.
It is likely that malachite green will be banned in the near
future
Malachite green is de-activated by light
Malachite green is reported to be toxic to tetras, catfish and
loaches and small marine fish
Formalin should be stored in the dark and above 40C
to prevent the formation of paraformaldehyde
Formalin is extremely irritation to gills and should not be
used where there may be existing gill damage or where skin ulcers
are present.
Dosage
rates:
Formalin: Used against protozoan
and metazoan parasites.
To prevent any misunderstandings, formaldehyde is a colourless,
highly toxic gas. Formalin is a 37 - 40% aqueous solution of
formaldehyde (which equals 100% formalin). It should not be used if a
white precipitate of paraformaldehyde forms in the container.
Paraformaldehyde is extremely toxic to fish. Keep formalin away
from light. Be extremely careful when handling.
Bath: 0.15 to 0.25 mls per litre for
up to 60 minutes.; Can be used on consecutive days for
a maximum of three treatments. Can irritate gills so it
should not be used where gill disease is suspected. Aerate at all
times. In most cases the lower dose should be used although the
high dose may be required against Epistylis
Prolonged immersion: 0.015 to 0.025
mls per litre. Repeat every 3 - 4 days and do a partial
water change between treatments. Maximum of three consecutive
treatments. Aerate at all times. Do not use where gill disease is
suspected.
Malachite green: Used
against Saprolegnia (fungus), water moulds and protozoan
parasites.
A zinc-free grade must be used. This is usually mixed as a stock
solution that will then keep indefinitely. The exact mixture of the
stock solution varies depending on preference. The main point is that
whatever concentration is used it should be easy to calculated many mgs
of malachite there are per ml of solution. A popular stock solution uses
20 grams malachite per litre of distilled water. This gives 20 mg
malachite per ml of stock solution. Using this stock solution.
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Bath: 1-2 mg malachite per litre water
for 30 - 60 minutes. Higher dose only for large fish,
such as koi, in hard water. This equates with 1 ml stock
solution per 20 - 40 litres of water. Can be repeated every other
day for a maximum of four treatments. |
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Prolonged immersion:0.1- 0.25 mg
malachite per litre: Repeat every three days for a
maximum of three treatments. This equates to 1ml of stock solution
per 80 - 200 litres. Again the higher dose should only be used
with large fish, such as koi, in hard water. |
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Topical treatment: The
stock solution can be applied directly to a wound, particularly
when fungus is present. Keep away from the fish’s eyes and
gills. |
Malachite and formalin mixture
(Leteux-Meyer mixture) Used against protozoan and metazoan parasites.
There are several variations. Two commonly used mixtures are:
Strong mixture: 3.68 grams
of malachite green dissolved in one litre of formalin: This is
used at 0.025 mls per litre of pond water for 60 minutes bath.
This stronger dose can also be used for stubborn parasites on koi
in alkaline water as a prolonged immersion. This dosage equates to
0.025 ml/litre formalin and 0.1 mg. /litre of malachite green.
Weaker mixture: 3.3 grams
malachite green dissolved in one litre of formalin: This is used
at a rate of 0.015 mls per litre of pond water as a prolonged
immersion for general pond use. This equates to 0.015 mls/litre
formalin and 0.05 mg/litre malachite green
See the fish
disease section for more details about specific parasites or diseases
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Useful conversions
are:
ppm =
mg/litre
i.e. 5 ppm = 5 mg / litre
mg / litre x
3.785 = mg / gall
(US)
i.e 5 mg / litre = 18.9 mg / gall (US)
mg/ litre x 4.546 =
mg / gall
(UK)
i.e 5 mg / litre = 22.7 mg / gall (UK)
To convert imperial
gallons to US gallons multiply by 1.2
Other useful
figures:
1 ounce = 28.35 grams
1% solution =
10 ml per litre
10 gram per litre
38 gram per
gall (US)
45 gram per gall
(UK)
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