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Most fish have an internal salt concentration of 1.0% or 10
parts-per-thousand (ppt) which is higher than their water environment.
Osmosis causes water to transfer from the lower salinity of the pond water
into the tissues of the fish. Addition of salt will lower the osmosis
pressure. This reduces the effort of the fish in eliminating the excess
water. The saved energy is then available for use by the fish’s
own immune system to fight diseases. On the other hand, if the salinity of
the water environment is close to the internal tissues of the fish, the
osmosis pressure will reverse and cause the fish to die of dehydration.
Salt concentrations between 0.3% and 0.5%(3 to 5ppt) will upset the
osmotic balance of some parasites i.e. the parasites’ cells will
dehydrate. Salt concentration of 0.3% are effective at detoxifying
nitrite and concentration of 0.25% or higher has been used to control
string algae. Nevertheless, salt can cause pond plant damage as the
concentration increases. Floating plants (water hyacinth, water
lettuce, etc.) are affected at lower concentrations than most bog plants.
SALT IN THE WINTER
Adding salt in the pond especially in the fall will
help fish survive the long cold winter months. We recommend adding 1.5 -
2.5 lbs of salt for every 100 gallons of water in the pond. We often add
salt in the fall, after taking out floating plants such as water hyacinths
and water lettuce.
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