Now that you’ve assembled your aquarium, you’re about to rush to the aquarium store to buy lots of cool fish. Not so fast! There are a few other issues to consider. What kind of fish are suitable for your aquarium? If it’s a small set-up, like a 10 or 20 gallon tank, you want to restrict yourself to small fish that are less than 3 inches in length. Also, get “peaceful” fish that are suitable for a community tank; stay away from aggressive species.
When you’re picking out your fish, be sure to ask about its adult size and temperament. A good aquarium store will be able to advise you on your selection. And if they can’t, do your shopping elsewhere; you want an aquarium store with staff who are well-versed in fish-keeping. When picking out your fish, make sure the fish in the store tank are healthy. If they appear inactive and emaciated, I recommend you leave that store and never return — I would never do business with a store that cannot properly care for its animals.
Don’t buy all your fish at once. Start off with two to four small fish, and keep them in your aquarium for about 2 weeks. There’s a very important reason for this. Remember the biological filtration I mentioned earlier? Fish waste contains ammonia. What your tank needs is a certain type of bacteria to break the ammonia down into less harmful components (nitrates and nitrites). This ammonia-zapping bacteria is airborne everywhere — it just needs time to settle down in your tank and multiply. When too many fish are introduced to a new tank, the bacteria will be unable to keep up with processing the ammonia. The ammonia and nitrites will build up to dangerous levels and eventually kill the fish.
This settling-in phase for the bacteria is called “cycling.” During the first few days, you’ll notice the water getting slightly cloudy-white. Not to worry–that’s normal and will clear away in a few days. After the initial cycling phase, you can start adding new fish. But do it slowly, about 3-4 small fish, or 1-2 medium-sized fish, every two weeks, to give the bacteria time to multiply and keep up with the additional load of fish waste. So, how many fish can you keep? The general rule is “one inch per gallon.” Therefore, it’s real important to know in advance how large your fish will get before purchasing them.
By the way, don’t just dump the fish you bought from the bag to the tank. New fish need time to acclimate to their new home because the water conditions in the store tank are slightly different from your tank at home. When you bring new fish home, first let the bag containing them float in the tank for about 15 minutes; this is done to let the water in the bag slowly reach the same temperature as the tank water. Then, open the bag and ladle out some of the water. Replace the quantity you removed with some water from your tank. Repeat this process about three to four times, about 10 minutes apart. This will help the fish gradually adjust to the slightly different pH of your tank water. To release the fish, gently tip the bag and allow the fish to swim into your tank. The fish will be quite stressed at first, and may hide for a couple of hours. But they will eventually get used to their new home, and start exploring every nook and cranny.