Unfortunately, it's quite common for fish to die shortly after being brought to their new home from the pet store. While many new fish owners are quick to blame the pet store for selling fish in poor health, in reality, this untimely passing is a result of budding aquarists not knowing how to properly acclimate aquarium fish to their home aquariums.
Most people just float the bag in the tank to equalize the temperature and then dump the fish, water, and all, into their tanks. Not only is this not the way to do it, but dumping the water into your tank is just begging for diseases and parasites that live at the fish store, with all the fish packed into the dealer's tanks, to take up residence in your beautiful community tank at home.
All new fish being put into a community tank should be quarantined for two weeks, at least, but that is a topic for another sticky. If you don't have extra tanks to quarantine in, you must be very observant of the dealer's tanks and the conditions therein. If there are sick fish, dead fish or ich on ANY of the fish in his tanks, do not buy fish there and put them in your community tank. They MUST be quarantined to protect your little beauties at home.
More Than Floating
The first thing you do is take off the rubber band and open the bag. Place it in the tank, so the water supports it. Next, roll the open top of the bag down four or five turns, so it creates a ring of air trapped in the rolls of the plastic bag. Now the bag will float on its' own without tipping over. If it is still unstable, a couple more rolls might be needed.
Now, while the temperature is equalizing, you need to test the pH of the water in the bag. That's right, test the water in the bag. You need to know how much different the pet shop water pH is from the pH of your home tank water. If you don't know the pH of your tank water, now is the time to test it.
If the two pH's are very close (within one or two tenths), this will only take about an hour. If the pH's are off by more than .5 up to 1 or even 1.5, this will take longer. Remember, you are giving your fish the best chance of survival in your tank. You could even drop a few crystals of ammo-lock into the bag to absorb any excess ammonia if it was a long trip from the fish store.
Why Does pH Matter?
OK, let's say that the difference in your pH to the bag pH is .8. Doesn't seem like much, does it? Well, it is! As little as a .5 difference, can and will send your fish into pH shock. This is something they may recover from, or may not, depending on the severity of the difference in pHs. The bigger the difference, the more chance of your new fish dying from it.
More new fish have been killed by pH shock than from any other problem after adding them to a tank.
Now to the procedure for acclimatizing. Using a 1/2 cup measuring cup dip 1/2 cup of tank water from the tank and add it to the bag. Now wait 15 minutes and do it again. With a .8 difference like the one we mentioned previously, you will need to do this every 15 minutes for at least TWO HOURS. That is eight times before you net them out and release them in the community tank. This assures that the water is very slowly changed from their bag pH to your tank pH without any abrupt shock to their little fishy systems.
With a difference of less than .4 you can drop the time to one hour, but with a larger difference, like 1.0 or larger, you will need to increase the time to 3 hours or longer and maybe even use a 1/4 cup measuring device to add less water each time for a longer period. I have taken up to 4 hours acclimating a very expensive, delicate fish to my quarantine tank. Discus are a prime example of a fish that needs a long acclimatizing period even though the bag water may be close to your tank water.
This will give your new fish the best chance for survival in your tank, although it will not protect your other fish from any diseases or parasites that the new fish may be carrying.
Remember, the temperature is the least of your worries when acclimatizing a new fish. Also remember, your new fish's life is in your hands, and he depends on you to make the right decisions.