One challenge you will face when designing your aquatic community is figuring out which fish can live together in the tank without causing problems. This is not always simple or obvious. While you should definitely research your species of interest, it’s easiest to start building your list by consulting a fish compatibility chart. Stop by to see our compatibility charts.
What are compatibility tables?
A compatibility chart is simply a chart with a list of fish, invertebrates, or plants on both axes or sides of the chart. Each animal or plant is then ranked against one another in terms of compatibility, or whether they can co-exist in the same enclosed habitat. The classification method varies, but generally includes Compatible, Incompatible, and Maybe.
Depending on your level of focus, compatibility charts give you a quick look at how different species or breeds tend to get along in a typical community setup. They may cover a wide range of aquatic organisms, such as tropical or community fish compatibility charts, or have a narrow focus, as with a wrasse or cichlid compatibility chart.
How to use compatibility tables
These charts are very helpful when planning your freshwater, brackishwater, or marine reef communities because they can help you quickly build a list of possibilities. However, you will still need to research each species, especially if you are interested in including many that are classified as cohabiting Perhaps or Marginal.
While the details vary depending on which chart you’re referring to, in general. Compatible fish are safe to keep together under most conditions, while Incompatible fish rarely work when housed together. Marginal species may be fine in some situations and a disaster in others.
Factors that determine compatibility
There’s more than one factor to consider when creating a compatibility chart, and that’s why you’ll want to follow up with more in-depth research rather than relying entirely on a chart for your final purchase decisions. The tables give you a rough idea of what might work if the conditions in your tank allowed it.
The weight given to each factor also varies by aquarist and the species being compared. In the end, the conditions and setup of your aquarium will be the determining factor in whether or not a group of fish get along. The most reliable charts are built considering the following factors:
The temperament of each species is probably the most important factor for them to get along in your aquarium. Aquatic organisms are generally classified as peaceful, semi-aggressive, or aggressive, and their compatibility is segregated along these lines. Some fish are also territorial and will defend one area of their tank from others.
You need to take your fish’s temperament seriously. While some semi-aggressive species, such as the Tiger Barb, may live in a peaceful community for a while, this is usually a temporary condition. Things will be fine until you wake up one morning to find your barbs fighting each other and your other fish.
One thing to keep in mind when looking at a chart is how focused the list is. A table that lists «cichlids» or «spikes» as incompatible may be ignoring the few peaceful breeds between them, such as the cherry spike and the dwarf cichlid. You may need to consult a barb or cichlid aggression chart for deeper details on your compatibility.
It’s always a good idea to balance the activity levels of the fish you select for your community and make sure they don’t conflict. Activity level generally takes into account how fast a fish swims and whether it prefers to hide or school together in a group. Active fish may annoy or stress less active or territorial fish with their antics.
Fish are generally classified as cold water or tropical species based on their preferred temperature range. In general, keeping cold and tropical species together is not recommended and most charts list them as incompatible.
Keeping fish or invertebrates in water that is too hot or cold for them can cause stress and illness, and usually leads to death. But some technically incompatible species have overlapping temperature preferences, and as long as they’re not incompatible in other ways, you might be able to manage them together in a tank.
Size can influence compatibility in many ways, and it really depends on the species being considered. Some species are better kept with others of the same size because they become aggressive towards those larger or smaller than themselves. Others target species in their size range, but leave smaller or larger fish alone.
The gender of your fish is not usually a factor in their overall compatibility, but it does depend on the species. In some cases, most notably the betta, one gender may be aggressive or territorial while the other is less so or completely peaceful. They can be classified differently in terms of compatibility, which you will need to be aware of.
Diet is not usually a major factor in compatibility, as long as each species is provided with the variety of nutrients it needs. Aquarists often provide a combination of commercial and fresh/frozen diets to aquariums in their community. But some species have a very limited range and are more difficult to keep in mixed tanks, such as the bamboo shrimp.
Other water conditions
Compatible species must have overlapping requirements in terms of water pH and carbonate hardness. Obviously, a species that prefers very hard water is not likely to thrive in a soft water aquarium, even if the fish mix were compatible in terms of temperament and activity level.
This is often an important factor in designing marine compatibility tables, but is generally less important in freshwater tanks. Corals and saltwater fish can have dramatically different preferences for hardness and pH, but most freshwater species have a wide enough range to be less of a limitation.
Tips for Managing Aggressive Behaviors
Aggression between community members is the most common problem we see in our community tanks and it can be incredibly frustrating. Even sticking with species listed as compatible is no guarantee that you won’t run into problems, and if you mix a lot of fringe fish, there’s a good chance you will.
Besides checking compatibility charts and researching your fish, what can you do to reduce the chances of aggression in your community?
These are my tips:
Give each fish plenty of space
The general rule of thumb is to allow about an inch of fish per gallon of water in the tank, but more space is always better. Use the size of the adult fish when calculating your capacity and not the size at the time of purchase. Otherwise, they could outgrow your tank as they mature.
Also note the recommended tank size. If your species needs at least a 20-gallon setup, then a 20-gallon community tank probably isn’t big enough for them long-term.
Create different zones in your tank
Use plants and decor to divide your tank into different areas to suit the activity level and territorial nature of your community. Give your fish in active formation room to swim and give your shy bottom feeders plenty of places to hide.
Choose species that prefer different areas
It can be easier to manage aggression when each species has a different area of the tank that they like to hang out in. Get a mix of bottom dwellers, mid-tier explorers, top-tier schoolboys, and fish that use up the entire tank. Don’t add too many territorial fish unless you have room for them to keep separate areas.
Be careful when adding fish to an existing community
Keep in mind that adding new fish to the mix could completely change a marginal situation or create conflict when members of the same species are different sizes. For example, the Tiger spikes on my 55 gallon community tank were fine for years until I added some new, smaller spikes to the bunch.
That changed the dynamic enough for everyone to start beating up the rest of the community. Despite my efforts to restore harmony, I ended up having to run a tank just for the spikes. Even peaceful fish can have conflicts over incompatible territory, food, and activity levels.
Freshwater Compatibility Chart
Our freshwater compatibility chart covers the most popular groups of aquarium fish and invertebrates, although we encourage you to do more research before making your final selections.
Saltwater Compatibility Chart
Our marine compatibility chart covers the most popular saltwater fish, invertebrates, and corals/live rocks, although we encourage you to do more research before making your final selections.
Compatibility charts for freshwater, brackishwater, and saltwater aquatic species can be very helpful when planning a community aquarium. You can use them as a guide while making an initial list for a new tank in the design process or making adjustments to an existing community.
They can quickly help you create a list of possible options, but you’ll still need to do more research to make sure the fish under consideration will thrive in your tank’s unique conditions. I hope you have enjoyed learning about fish compatibility and would love to read your comments and suggestions here or on our social media pages.