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Temperature difference
Fish generally are very intolerant of rapid changes in their water conditions. A
sudden change in pH or KH can result in stress and illness. However, by far the
most important factor to consider is the change in temperature. A five degree
sudden change in temperature can be enough to cause most fish so much
stress that they are likely to die within a day of the change. For this reason, we
will always float fish.
If you have ever seen your local fish store on the day of a delivery, you will
hopefully see that there are many bags with fish floating in the tanks that they
will be kept in until sold. Fish stores have a lot to lose if a whole batch of fish
suddenly dies from stress, and so they will usually take care to acclimatize their
fish correctly. Floating fish in bags or containers such as plastic boxes or
breeding isolators means that they will gradually become accustomed to the
temperature of the tank. A fish should be floated in darkness for at least fifteen
minutes. I personally float my fish for anything up to thirty minutes. While it
seems to make sense to float a fish for as long as possible, to reduce the stress
of transportation and temperature difference, don't forget that the fish is currently
in a rather cramped environment, and a balance of introduction speed to
temperature acclimatization needs to be found. For me, thirty minutes is perfect.
It is also important to remember that even if the water in the transport container
feels like it is the same temperature as your own tank, your fish will like a rest
from the transport itself, and temperature is not the only thing to consider.
Water Conditions
Now that your new addition is used to the temperature of your aquarium, you will
need to gradually add small amounts of water from your tank to the transport
container. If the transport container currently has a fish in four cups of water,
then you should add one cup of water from your own tank to this container every
five to ten minutes. You should aim to add, gradually, the same volume of water
that is in your transport container from your own tank over a period of fifteen to
twenty minutes. Once you have done this, then it is on to the method of
introduction.