Your friend had just given you his empty aquarium and other equipment for fish keeping after his Oscar fish of 10 years had died. You were so excited to get into the fish keeping hobby and decided to buy an Oscar fish just like your dear friend once had. You went to a pet store right away and picked the cutest and healthiest-looking Oscar fish. Your eyes were sparkling as you watched the staff put little Oscar inside a plastic bag. Slowly, you walked home as you carefully wrapped your hands around Oscar’s plastic bag. Finally, you reached your apartment and put the plastic bag on your desk. You stared at all the paraphernalia lying on the floor. You scratched your head as you tried to figure out what to do next. Then it hit you: you didn’t know what to do!
I hope you’re not in such situation. In this article, I’ll teach you the crucial step in fish keeping - introducing your new fish to your new aquarium. This step is crucial because it determines whether your fish will make it through or not, and if you messed up, you might even be disheartened to continue this wonderful hobby. I’ll present to you the methods that hobbyists have been using. 

Before Bringing Your Fish Home

Aquarium SetupCredit:

set up your aquarium
Photo: BigGirlBlue | Flickr

Wash the aquarium, the filter and the filter media, the decorations, the gravel, and other equipment that you will be using. Do not use detergent in cleaning the equipment. Set up the aquarium and fill it with dechlorinated water (more on this later). Turn on the filter to start the cycling. Monitor the ammonia and the nitrite levels using your testing kits. Once cycling is completed, you’re ready to bring your new pet home.


Chlorine and Chloramine

Chlorine kills bacteria. It is added to tap water to make it safe for humans, but not to your fish. Chlorine kills the beneficial bacteria that you have been trying to establish in your aquarium (the beneficial bacteria “clean” the tank water and make your fish healthy and happy). You can get rid of chlorine by adding dechlorinator or chlorine remover to your tank water.  If you want to remove chlorine without adding dechlorinator, fill a clean bucket with tap water and leave it for 24 hours. The chlorine will evaporate. You can also add an air stone in your bucket to remove chlorine more thoroughly. However, another chemical known as chloramine is sometimes added to tap water. It is a compound composed of chlorine and ammonia that cannot be easily removed through evaporation. If you have researched about fish keeping, you will know that every hobbyist is allergic to the word ammonia. Ammonia can kill your fish and plants. You wouldn’t want that to happen in your aquarium.
You can ask the water supply in your area to find out what they have added to the water. Nevertheless, it is always recommended to add dechlorinator to be on the safe side. Dechlorinator can remove both chlorine and chloramine in just a few minutes. Another alternative is to clean the water through chemical filtration (a type of filtration that removes chemicals and medicines from your tank water). Fill a container or a spare aquarium (without fish) with water and install a chemical filter in it. Turn it on for 24 hours to remove both chlorine and chloramine.
Dechlorinators are available in pet stores. These are sometimes known as water conditioners, which is a more general term that can also refer to other chemicals added to your aquarium. There are many types of dechlorinators. Some have additives such as stress relievers and vitamins and these types are more expensive than the standard ones. Some sources claim that these types of dechlorinators can cause problems in the long run and are therefore, not necessary and are impractical to use.

Introducing Your Fish to a Cycled Aquarium

Adding New FishCredit:

leave the plastic bag in the aquarium for
about half an hour
Photo: Nat Tarbox | Flickr

When you buy a fish, the staff will put the little fellow inside an oxygenated plastic bag. If you have a lighting fixture on your aquarium, turn the lights off as not to alarm the fish. Then, put the plastic bag into your aquarium and leave it floating for about half an hour. Why? This is to acclimate the temperature between the tank water and the water inside the plastic bag. You cannot take a fish from a 28°C water and transfer it to a 20°C water. Doing so will result in temperature shock to the fish. The same rule applies to water changing. You cannot add very cold water into the warm tank water (and vice versa). The temperatures should be as equal as possible. Going back to the new fish in the plastic bag, after half an hour or so, open the bag and slowly add the tank water into the plastic bag. This will allow the fish to gradually adapt its body to the water conditions outside the plastic bag. Leave it there for another half an hour. Be careful not to spill the water from the plastic bag into the aquarium. You wouldn’t want to contaminate your aquarium with the water from the store. After that, your fish is ready to get out of its plastic bag. Scoop your fish out of the plastic bag and release it into its new home. Turn on the aquarium lights after a few hours (or leave them off if it’s nighttime).


Introducing Your Fish to a Not-Yet-Cycled Aquarium

Set up your aquarium. Pour in dechlorinated water and turn the filter on. If you have other existing aquariums in your home, you can take a few pieces of filter media from it and use it in your new aquarium. The existing beneficial bacteria in the filter media will help cycle your new aquarium more quickly. Buy a hardy fish* and introduce it to your aquarium the same way as you would with a cycled aquarium.

*Hardy fish, also called starter fish, are fish that are tough such as cichlids, catfish, gouramis and tetras. I encourage you to research first about the specific fish in your mind to make sure that it can be used as a starter fish. Do not use a goldfish to cycle your aquarium, unless you want a goldfish for your aquarium. They are not as tough. Goldfish require different kind of care. An aquarium that has been cycled using a goldfish may not be a suitable home for your tropical fish.


How Many Fish Can I Add to My Aquarium?

Beautiful AquariumCredit:

How many fish can your aquarium carry?
Photo: Reggie Alvey | Flickr

For not-yet-cycled aquariums, you can add a couple of fish at a time. Wait for 3 to 6 weeks before adding new fish. Adding too many fish at once will produce more wastes, thus, stressing the beneficial bacteria that are yet to be established.

To know how many fish you can put into your aquarium, first, you have to find out how many gallons your aquarium can carry. Multiply your aquarium’s length, width, and height and divide the product by 231. You can have 1 inch fish for every gallon (e.g. around 20 one-inch fish for 20-gallon tank). However, remember that this is only an estimation. Round-bodied fish produce more wastes than their thin-bodied counterparts. You have to keep an eye on your fish. Monitor your aquarium’s nitrite and ammonia levels regularly. Moreover, find out the adult size of the fish you’re getting. You wouldn’t want to stock your 20-gallon tank with 5 three-inch baby parrotfish only to find out that each could grow up to 10 inches long.
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