Adding Fish to an Aquarium

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Considering the fact that an aquarium without the fish is a pretty boring view, everyone who has one is probably thinking of adding some fish.

This entry will guide you through the process.

Preparing a new aquarium

First of all, if you have a new, fully setup but uninhabited aquarium, you have to know how to prepare it for the fish that are going to move in.

The first thing, which should be quite obvious, is to fill it with water to about five centimeters below the top. There are, however, some plants that prefer a lower water level, so be sure to check that.

After you do that, lots of things will happen. First, the chlorine used to disinfect tap water will have to get out, because it is incompatible with any life. This will happen in about a day.

Then important bacteria1 will start moving in. This will lead to a slight darkening of the water. When, in a few days, it becomes transparent again, this phase is done.

If you want to grow aquatic plants in your aquarium2, now is the time to add them.

Just to be safe, it would be good if you wait for about three more weeks. People are usually impatient when they want to finally have some fish, but please don't be too hasty about it. During that whole process keep your filter running. The good bacteria like that.

Estimating the maximum capacity

The maximum number of fish that an aquarium can support is very specific, and being able to estimate it would require some experience.

Here are, however, some basic guidelines. The most important factor is probably the capacity of the fish tank. A fish with an average size would require about 3 litres of space, but don't take it as an exact formula.

After you've calculated the number of fish in that way, be advised that this number is increased by the presence of (and therefore decreased by the lack of) a good filter, healthy live plants. Doing regular water changes would also increase the maximum load of your aquarium.

Another thing you should be aware of: do not add too many fish at once. It's best to add at most two at a time, and to wait until they've adapted to their new environment before adding more. An exception may be made for schooling fish.

Choosing fish

Choosing a good species of fish to start with is important. Some fish are really hardy, and others are extremely sensitive.

It is best to ask the people at the aquarium store about the requirements of each fish and its compatibility with other species. If they don't seem to be very competent about it, it's a good idea to buy your fish from somewhere else.

Not every two species of fish can live together in an aquarium. Different fish have different requirements on water hardness, pH, temperature, etc. It is not, however, a large issue if the difference in their requirements is small, but you obviously cannot mix freshwater and saltwater fish, or goldfish and tropical fish.

It is more important to have in mind the behaviour of the fish. Some are peaceful and can be kept with any other fish. Others are very aggressive under some conditions. There are also schooling fish, which only feel comfortable in large groups of the same species.

If you are going to have a species aquarium, you won't have to worry about fish compatibility, but it is important to choose a good ratio of males to females. Again, this is very different for each species.

Finally, adding fish!

So, your tank is setup and ready to accept its new dwellers, you've bought the fish you are going to add, you've transported them3 to your home, and you are ready to put them in.

Fish usually come in small plastic bags. Here is what you should do to move the fish from the bag to the aquarium:

  • Put the bag with the fish inside the fish tank so that it flows on the surface
  • Wait about 15 minutes until the temperature in the bag and in the tank is balanced
  • Remove one quarter of the water in the bag and replace it with water from the aquarium
  • Repeat the previous step each 15 minutes until all the water in the bag is replaced
  • Finally, release the fish and let them get acquainted with their new home!
1These bacteria are needed to process toxic waste substances in the aquarium.2Which is, generally, a very good idea, as plants don't only serve a decorative purpose.3Be careful when transporting fish during the winter, as they can, well, freeze.

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