One challenge in choosing aquarium fish is to pick ones that will get along in the tank. We all want a variety of different kinds to make the tank more interesting to look at, but you need to be careful that the types of fish you are choosing won’t be picked on by those you already have or vice versa.
The key to choosing aquarium fish for a successful and harmonious tank is to buy only aggressive fish or only peaceful fish, or if you are mixing the two make sure the aggressives are much smaller than the peaceful ones. Add the mildest most peaceful fish first, then a couple of weeks later you can add some that are a bit more aggressive but make sure they are smaller. Two weeks later add some that are even a bit more aggressive but smaller. Keep adding in this manner until you have enough fish (about 1″ of fish per gallon). Keep an eye out to make sure that one of the more aggressive fish is not tormenting the others and that all your peaceful fish don’t have to spend all their time hiding from the last 2 you put in.
The safest method, of course is simply choosing aquarium fish that get along. One of my favorites is Neon Tetras and I always thought a tank would look quite smashing with just a large school of these fish. If, however, you want something else to look at besides your neons, these fish get along with Fancy Guppies White Clouds, Glass Fish and Honey Gouramis. None of these fish get along so well with any other kinds of fish, but you could set up a pretty nice tank with just these species.
Some of the mildly aggressive fish that can be put in a tank together, but won’t mix that great with other fish include Gouramis, Angel Fish Loaches, Tiger Barbs and most Sharks. These fish like to be kept in schools so ask the owner of the pet shop how many he recommends having in the tank.
Cichlids are aggressive but can be very beautiful for fresh water fish. They are typically large in size and some are silvery shiny which reflect a beauty underwater. They shouldn’t be kept with the more peaceful fish, unless you want to be digging dead fish out periodically. Some common cichlids include Jack Dempsey, Pink Convict, Firemouth. You can mix these with sharks and catfish. Some of the more aggresive African Cichlids need to be kept in large groups of 6 or more in order to keep balance and order in the tank.
When choosing aquarium fish with long fins, you may want to keep to mixing them with the more peaceful species. As we all know, bettas are quite beautiful but can only be kept 1 per tank (unless you have a very large tank and then you might be able to get 2 to co-exist). They can be kept with swordtails, platies, mollies, angel fish and gouramis.
Of course, you need a fish to clean the tank and you can use a chinese cat fish or plecostomus for this. I have mixed these kinds of fish in all different tanks with no problems but have always kept to only 1 plecostomus per tank.