Someone came up with this idea once that you should at least one gallon of water per inch of fish, but there are so many exceptions to this rule, that I am not even sure if this still applies. According to the old rule, if you had three fish that are one inch each, you should have at least three gallons of water. However, the problem is that all fish start out small and need room to grow. Some people also believe that a fish will only grow as large as the tank will allow it to. This is simply not true either. For example, if you take a Betta and put it in a small bowl with one liter of water, it will eventually out grow that bowl.

Bettas are the only types of fish that can actually survive for long periods of time in such a small amount of water,. This is because they can breathe both water and air. As far as freshwater fish go, it really depends on the the size and the type of fish. There are several species of fish that should never be put together in one tank. Most people are aware that you should not put two male Bettas together. These kinds of fish will fight, and in some cases, one will eat the other one.

The same is true for some other types of fish as well. Larger varieties of goldfish will eat some smaller varieties if the smaller fish can fit in the larger fish's mouth. Goldfish are one type of fish that almost never get along with any other variety of fish. There are a few exceptions to this, but goldfish should generally be kept with other goldfish.

The preconceived notion that you can keep a goldfish in a small bowl is also not true. Goldfish need much more space than most people realize. For most varieties of goldfish, there should be at least ten gallons of water per fish. So, if your niece has a ten gallon tank and wants to put goldfish in it, she should only keep one in it at a time.

For a tank this small, I would recommend something much smaller and less demanding. Guppies are easy to care for and you can house 7-8 of these in a tank of this size. When it comes to introducing fish to the tank, you should always add only one fish at a time. Set up the tank first, make sure that all filters and aerators are working properly, and allow the tank to cycle without any fish in it for about 3-4 weeks. After this, find one fish to add to the tank. When adding additional fish, quarantine them in a large bucket or separate tank before introducing them in case of parasites.

There is a chart listed in the sources that will help you determine which types of fish are compatible with each other.

It depends on the type of tank she wants. You have to decide on the species of fish you want and what size they can grow to. Fish will grow into their surroundings and by how much you feed them. For a small tank like this it also depends on the type of fish you get. Solitary fish, like angels, need more room then fish that swim in schools, like neons. If you are mixing the species youshould give about a gallon of water for each fish. Remember to take away for the room taken up by decorations.