Getting Started: Adding Fish and Stocking your Tank

So, finally you are ready to add fish to your new aquarium! You bought your fish tank and all the equipment you need, you set it up in your home, you cycled the tank using a fishless method and you cleaned it up to make it ready for your new pets. During that time you researched your water parameters and what fish you can successfully keep in your aquarium. So what is the best method for adding your fish to their new home?

When you buy your fish, the pet store should put them in a bag about ½ full of tank water from the pet store. Without opening the bag, float it in your tank for about a half an hour to let the temperature equilibrate. After that amount of time, carefully open the bag and add a quarter to a half of a cup of water from your tank to the bag. Do NOT put any water from the bag into your tank, as it may have parasites or diseases you don’t want in your tank. If you need to remove any water to make room, pour it (carefully and through a net so as not to lose any fish) down the drain. Close the bag back up again and let it float for another 15 minutes. After 15 minutes replace another quarter to half cup of water from the bag with an equal amount from your tank, and let it float another 15 minutes. At this point, examine the fish in the bag. If any have died, take them back to the pet store and explain what happened. If they all look alright, use your net to get the fish out of the bag and into your tank with as little store water being transferred to the tank as possible. Monitor the fish carefully for the next couple weeks, and don’t feed them for at least half a day. Being introduced to a new tank is very stressful for your fish, so they are not likely to eat, or if they do, to fully digest their food until they have settled in.

When stocking a fish tank, you do not want to add more than a couple fish at a time, though you can get away with more if the fish are small and you have a large tank. Basically you don’t want to overload the biological filter with a ton of waste produced by many fish. Add 2 medium sized fish or up to 4 small fish, and monitor the ammonia and nitrite levels for the next week to make sure your biological filter is handling the new source of ammonia. If the levels remain undetectable for a week, you can safely add another batch of fish.

One of the mistakes most beginners make when setting up an aquarium is overstocking the aquarium. Fish need plenty of room to move around, and many species are territorial. This means that putting many fish into a too-small aquarium will cause stress, which as you know by now increases the risk of disease and death in your fish. The rule you will most often hear is you should have 1 inch of fish per gallon of water. Most people do not follow this, but even if they do, they are not following it correctly. One inch of fish per gallon of water applies to thin fish, not fat ones. Examples of fish this rule works for are guppies, neon tetras, white cloud minnows, etc. For medium bodied fish, like Cory cats, barbs, platys, etc., you need 2 gallons of water per inch of fish. Fat fish are fancy goldfish, piranhas, Oscars and similarly shaped fish, and they require 3 gallons of water per inch of fish. While there is some wiggle room if you have lots of healthy plants or you like doing frequent water changes and keep your filter clear of gunk, this is a rule you should adhere to at least until you learn more about fish keeping.

People also violate the 1 inch per gallon rule (or 2 or 3 inches, depending on the fish) when they go by the current length of their fish, rather than basing the number of fish they buy on the ADULT length. A goldfish may only be 2 inches when you buy it, but it can grow up to 8 inches to a foot in length. This means you can’t put 5 2-inch goldfish in a 30 gallon tank, as they will quickly outgrow the tank. When stocking your tank with any fish, you need to determine what the maximum length of the fish you choose will be, and stock the tank based on that. Overstocking will likely overload your biological filter, and will certainly cause more stress on your fish than keeping the tank stocked at a proper level.