Freshwater Fish Compatibility Chart – A Complete Reference Guide

Last Updated: May 16, 2026

Fish compatibility is one of the first things I look at when helping someone stock a new tank, and it’s where a lot of beginners go wrong by trusting the fish store without checking the numbers. After 25 years of keeping community tanks and fielding compatibility questions from my YouTube audience, I’ve developed a clear decision framework for stocking. A chart is a useful starting point, but it will steer you wrong without understanding the four factors that actually determine whether fish can coexist.

No chart can tell you if two fish are truly compatible. You still have to think through the variables. This guide gives you both: the charts and the framework to use them correctly.

The Four-Factor Compatibility Framework

Before you look at any chart, run through these four factors in order. They are listed by priority. If a pair of fish fails the first check, the rest do not matter.

Water Temperature: The First Cut

This is the check most beginners skip, and it causes more stocking failures than any other single factor. Here are the ranges you need to know before buying anything:

• Cold water (60 to 72°F / 16 to 22°C): Goldfish, white cloud mountain minnows, weather loaches
• Standard tropical (72 to 78°F / 22 to 26°C): Most community fish – tetras, barbs, corydoras, livebearers, rasboras
• Warm tropical (78 to 82°F / 26 to 28°C): Discus, rams, many South American dwarf cichlids, altum angelfish
• African cichlid range (76 to 82°F / 24 to 28°C): Overlaps with warm tropical, but chemistry requirements don’t

Goldfish and tropical fish is the most common beginner mistake. A goldfish needs 60 to 68°F (16 to 20°C) to thrive. A betta needs 76 to 82°F (24 to 28°C). There is no temperature where both are genuinely comfortable. One or both fish will be permanently stressed.

pH and Water Chemistry: The Second Cut

Most community freshwater fish tolerate a pH range of 6.5 to 7.5. The exceptions are the ones that cause problems when mixed incorrectly.

• Soft, acidic water specialists: Discus, cardinal tetras, most South American dwarf cichlids (apistos, blue rams). Target pH 5.5 to 6.8, very soft.
• Hard, alkaline specialists: African cichlids (Lake Malawi, Lake Tanganyika). Target pH 7.8 to 8.5, very hard.
• Flexible: Most danios, most barbs, some tetras, livebearers (prefer slightly hard), corydoras. These fish tolerate a wide range and are the backbone of community tanks.

If you are keeping African cichlids, their tank mates need to tolerate hard, alkaline water. Very few community fish do. This is why most African cichlid tanks are species-only or cichlid-only setups. It is not just about aggression. The water chemistry locks out most other options.

Size and Predation Risk: The Third Cut

This one is simple in principle and endlessly ignored in practice. If it fits in the mouth, it will eventually end up in the mouth. This is true even of fish not generally considered aggressive predators. Angelfish are a good example. They are sold as peaceful community fish, and they are, until they are paired with neon tetras. Neons are exactly the size that triggers an angelfish’s feeding response. This combination fails routinely.

Size ratio guideline: if fish A is more than three times the length of fish B, fish B is at risk. At night, with lights off, fish A will investigate.

Temperament and Behavior: Using the Chart Correctly

Temperament labels on charts fall into three broad categories: peaceful, semi-aggressive, and aggressive. Here is what those actually mean in practice.

• Peaceful: Generally does not initiate aggression. Will still defend territory during breeding. Will still compete for food. May bully smaller or slower fish if they are significantly smaller.
• Semi-aggressive: May nip, harass, or outcompete tank mates depending on group size, tank layout, and individual personality. Tiger barbs in a school of 15 are very different from tiger barbs in a school of 5.
• Aggressive: Will establish territory and defend it, often with force. Some can be housed with tank mates that are similar in size and temperament; others (like most large oscars and jack dempseys) do best solo or in species-only setups.

Freshwater Compatibility Chart

Below is a general freshwater compatibility reference. Use it after running the four-factor framework above. Keep in mind that “C” (conditional) entries depend heavily on tank size, layout, and individual fish personalities.

Saltwater Compatibility Chart

Marine fish compatibility is more complex than freshwater. In a reef environment, fish are constantly competing for shelter and territory, which is a survival behavior hardwired from living in the coral reef. Even fish labeled as “peaceful” can be aggressive in the confines of a home aquarium.

Personalities vary more in saltwater fish than freshwater. A yellow tang can be genuinely peaceful in one tank and a tyrant in another. This is especially important when determining reef-safe status. Always check species-specific profiles before adding any saltwater fish to an established reef.

Tank Layout and Introduction Order

Two variables that charts cannot capture at all are how the tank is set up and the order new fish are introduced.

Layout matters for territorial fish. Cichlids, bettas, and many semi-aggressive species are significantly less aggressive in a tank with dense decoration that breaks line of sight. Rocks, driftwood, and plants create natural territory boundaries. A cichlid that would destroy tank mates in an empty 55-gallon tank may coexist reasonably well in a well-scaped version of the same tank.

Introduction order matters for established fish. Any fish already in the tank has established territory. Adding a new fish of the same species or similar temperament into established territory triggers aggression. The established fish sees the new arrival as an intruder. Adding multiple fish at once, or rearranging the tank before introducing new fish, resets the territorial dynamic and reduces fighting significantly.

Common Compatibility Mistakes I See Repeatedly

Introducing New Fish to an Existing Tank

The introduction process is as important as the species selection. A fish that would be compatible under normal circumstances can be rejected if introduced incorrectly.

The basic protocol: float the bag to equalize temperature, slowly add tank water to the bag over 15 to 30 minutes, then net the new fish into the tank without adding bag water. For more aggressive tanks, rearrange the decor before introducing the new fish to disrupt existing territory claims.

For any new fish, quarantine for 2 to 4 weeks before introducing to an established tank. This protects your existing fish from disease and gives you time to observe the new fish for illness.

FAQ

What freshwater fish are most compatible with each other?

The most universally compatible freshwater fish are those in the “flexible” chemistry category with peaceful temperaments: corydoras, most danios, smaller gouramis, peaceful tetras (not serpae), cherry barbs, rasboras, and otocinclus. These species tolerate a wide pH range, have similar temperature needs, and are not aggressive toward tank mates of similar size.

How do you know if fish can live together?

Run the four-factor check in order: temperature overlap, water chemistry match, size ratio, then temperament. All four need to check out before you commit. If any of the first three fail, do not add the fish regardless of what the compatibility chart says about temperament.

Which fish should not be kept together?

The most common incompatible combinations are goldfish with tropical fish (temperature), African cichlids with community fish (chemistry and aggression), discus with standard community tropicals (temperature and chemistry), angelfish with nano fish (predation), and bettas with fin nippers (harassment).

What is a good fish combination for a community tank?

A well-balanced community tank uses all three levels of the water column: bottom (corydoras, otocinclus), mid-level (tetras, rasboras, barbs, danios), and surface or upper-mid (gouramis, hatchetfish). Choose species with overlapping temperature and pH requirements. Stick to a consistent size range. Add a centerpiece fish (a single betta, a pair of angels, a small gourami species) if you want a focal point.

Does tank size affect compatibility?

Yes, significantly. Many compatibility problems are aggression problems driven by insufficient space. A pair of convict cichlids in a 20-gallon tank is a recipe for conflict. The same pair in a 55-gallon with proper layout may do fine. When in doubt, go bigger and add more decoration. Space and visual barriers resolve more compatibility issues than any other single factor.

Closing Thoughts

The charts in this guide are a solid reference, but they are a starting point, not a final answer. Run the four-factor framework before adding any new fish. Check temperature first, chemistry second, size ratio third, then temperament. A tank that passes all four checks can still fail due to individual fish personality, poor introduction timing, or inadequate layout. A tank that fails any of the first three checks will always fail.

When you are unsure, build the habitat first. The right hardscape, the right water parameters, and the right introduction sequence solve more compatibility problems than choosing a different species. If you have a specific stocking question, drop it in the comments and I’ll give you my honest read on it.

Quick Compatibility Reference

Fish Group	Temp Range	pH Range	Temperament	Compatible With
Community tropicals (tetras, rasboras, danios, corydoras)	72 to 78°F (22 to 26°C)	6.5 to 7.5	Peaceful	Most other peaceful community fish
Livebearers (guppies, mollies, platies)	72 to 82°F (22 to 28°C)	7.0 to 8.5	Peaceful	Community fish with similar hardness needs
African cichlids	77 to 82°F (25 to 28°C)	7.8 to 8.5	Aggressive	Synodontis catfish, similar cichlids only
Discus	82 to 86°F (28 to 30°C)	5.5 to 6.5	Peaceful	Cardinal tetras, altum angels (specialist only)
Goldfish	60 to 68°F (15 to 20°C)	7.0 to 8.0	Peaceful	Goldfish only. Not compatible with tropicals.