Freshwater Aquarium Fish Compatibility

Neon tetras in planted tank

Илья Голубев / Getty Images

When designing your ideal freshwater aquarium, start with what species you would like to have. If you've ever dreamed of your ideal aquarium, take some time and list out the species you would most like to have. Now, its time to consider a few key points in mixing species together in an aquarium.

Before You Get Started

Before you go out and purchase your desired fish, take some time to plan out a few key tank features.

Volume and Layout

Each fish species has specific considerations as to how much room one fish will need. And it may be a specific type of space, such as sandy, rocky, lots of plants or isolated caves. More community-oriented fish may like to live in large groups, while others may like to have a lot of room to themselves. Depending on what species you'd like to mix, take some time to determine how much space they would all need. Can you fit that volume and all their desired decor?

Water Quality Parameters

When it comes to freshwater fish, especially cichlids, some water quality parameters do not mix. If one species likes hard water with a high pH, and the other can't stand anything but low pH and soft water, don't try to balance them out in the middle. If the pH, temperature or kH (alkalinity) doesn't match, neither do the fish.

Aggressive Behavior

Aggressive nature is species-specific. Sometimes, captive bred individuals may be more accustomed to living in closer quarters, but this is not guaranteed. The more aggressive freshwater fish (link to other article) should be mixed very carefully. Always add the most aggressive fish last so other, less aggressive, but still ornery, fish can settle into their spots.


If you plan to breed your fish, make sure to have extra volume in your tank to keep your offspring! Breeding fish is a fun project for any fish owners, but keep in mind that some fish will become very aggressive over breeding areas. Different species will like different types of areas for growing their young. Be it soft sand, a large cave or low water flow area, be sure your tank has plenty of room for the parents to do their job and not aggravate their neighbors.

Ideal Freshwater Community Tank

In an ideal tank, all fish, regardless of their aggressive nature, would have room to live and thrive. Once you have matched your fish to their water quality parameters, maintaining good water quality will go a long way in keeping your tank healthy.

What Environment Is Best for your Fish?

Should it be rocky, sandy, planted or a combination? Depending on where your fish lives, how they forage for food and their breeding method, you may have to become an expect aquascaper to create the ideal underwater world for your particular fish combination. If you chose different fish species, would they be able to live in the same environment? Choose more community-minded fish that can get along in smaller space and enjoy the same environment, you may not have to divide a very large tank into different zones for different species.

Do Your Fish Eat the Same Diet?

Aggressive fish can be the biggest pain during meal times. If you have a wide mix of species and behaviors, feeding can be a complicated process. If you have a combination of species that are spread out across the herbivore, omnivore and carnivore spectrum, making sure each fish gets their intended diet can be a tricky, involved process. By choosing fish that eat a similar diet, you will be able to enjoy them more and worry less about who ate who's dinner.

Where your fish eat in the water column is a consideration few pet fish owners think about before starting their tank. Many freshwater fish will feed at the surface or throughout the water column. But bottom feeders, such as algae-eaters and loaches will often sift through the substrate for their meals. Can you guarantee that enough food will get down to the bottom of your tank? Spreading out meals throughout your tank can greatly help limit competition, just as long as everyone has enough to eat.

Best Freshwater Community Aquarium Fish

Neon Tetra (Paracheirodon innesi)

Bright and easy-going, the Neon Tetra is a great addition to any freshwater community tank. Although easy prey for more aggressive fish, Neon Tetras like to school together, don't require much space and are not picky eaters.

Two neon tetras
Neon Tetra Mirko_Rosenau / Getty Images 

Panda Cory Cat (Corydoras panda)

These small scavengers have a unique black and white color pattern, giving them the "panda" descriptor. Used to living in small groups of 6 or more, these fish will sift through fine substrate, collecting lost bits of food. They get along with many different types of fish, making them ideal community members.

Panda Cory Cats (3)
dangercorpse / Flickr / CC by 2.0

Platys, Mollies, and Guppies

The number of breeds and varieties of these live-bearing fish is immense. All of these varietals are easy going, community fish. However, keep in mind that live bearers will reproduce very quickly. Unless you can separate males and females, you will likely start out with many more fish that you expect. Many a pregnant mama has been adopted and given birth to multiples within days of being added to your tank.

Male guppy
Brian Kilford / Flickr / CC by 2.0

Fish to Avoid in Community Tanks (link to aggressive article)

Veil Angel Fish (Pterophyllum scalare)

Many a freshwater aquarist has started with a small group of easy-going veil angelfish and ended up with multiple angel fish tanks. Although they get along as juveniles, as they grow larger, most angelfish groups will start to have a dominant abuser. Once that fish has been removed, another will take their place, until you have multiple tanks of single fish.

Freshwater angelfish
Christophe Archambault / Getty Images

Bucktooth Tetra (Exodon paradoxus)

Don't let the "tetra" name fool you! These are not like their other tetra cousins. The Bucktooth Tetra is an obnoxious nipper that likes to try and take a bite of anything shiny that passes by, likely another fish! They also do not play well with their own kind, so give them plenty of room and only one fish per tank.

Bucktooth Tetra
bertrand.sant / Flickr / CC by 2.0

Convict Cichlid (Archocentrus nigrofasciatus) 

The Convict Cichlid is only one of many aggressive cichlid species. If you're looking to get into cichlids, there are many more species and personalities to get acquainted with before you start. Many cichlid species require a certain density in order to thrive. If you're a little under or over-populated, your fish will become more aggressive.

Convict Cichlid
wiljoj / Getty Images

Freshwater Community Aquarium Tips

It is always best to plan ahead! If you haven't purchased any supplies or equipment, start with a list of desired species and go from there. If you've already bought the tank, plan your species carefully.

If possible, always go with a bigger tank. This will give you room in case some of your fish don't read the rule book.

Always add the most aggressive fish last and give more timid fish lots of places to hide, and during feeding time, pay special attention to how your fish are behaving so everyone can get a fair share without being harassed.