Every saltwater fish species has their own minimum tank size requirements and compatibility/incompatibility profile when added to a tank with certain other species. That’s why I created the Saltwater Aquarium Blog Interactive Saltwater Fish Compatibility Chart and Tool.
Saltwater fish compatibility is as easy as 1, 2, 3
- Select 1–3 saltwater fish from the drop-down menu. I recommend you start out with just one fish, until you get used to the tool.
- (Optional step) Enter the size of your aquarium in gallons if you want the tool to edit the output based on size.
- Click the SUBMIT button to see your results.
Interactive Saltwater Fish Compatibility Chart and Tool
What determines saltwater fish compatibility?
While the compatibility tool provides quick answers, understanding why certain fish are compatible or incompatible will help you make better stocking decisions and troubleshoot issues in your tank. Key factors influencing compatibility include:
- Territorial aggression: Many saltwater fish defend a territory, especially in smaller tanks. For example, damselfish and some wrasses can become highly aggressive toward newcomers or similar-looking species.
- Feeding behavior and dietary competition: Fish that compete for the same food source may become aggressive or outcompete shyer tankmates, leading to malnutrition or stress.
- Size mismatches: Larger fish may view smaller fish as food, or simply intimidate them, even if both are considered “peaceful” species.
- Social structure: Some species thrive in groups (schooling fish), while others do best singly or in pairs. For example, anthias and chromis are generally peaceful in groups, but certain wrasses or dottybacks may fight if kept together.
- Habitat needs: Fish with similar shelter or swimming space requirements may compete for the same areas, increasing stress and aggression.
- Tank size and layout: Overstocking or insufficient hiding places can amplify aggression and stress, even among otherwise compatible species.
Compatibility is not a static list—it’s a dynamic outcome shaped by these variables and the unique personalities of your fish. For example, mixing similar-shaped tangs often fails due to territorial disputes, and overstocking any tank increases the risk of aggression and disease. Use the tool as a guide, but always consider these underlying factors when planning your community.
This interactive tool and saltwater fish compatibility chart will show you whether the fish group you selected is reef safe, and it will also show you the list of fish that are:
- Compatible with
- Not compatible with, or
- Compatible with caution
If this is your first time using the compatibility chart, I recommend you just select 1 fish, to get started.
If you chose more than one fish type, the results below are for the combination of fish on your list. For example, if you picked 3 fish, all of the fish listed in the “Compatible” column should be compatible with all 3 of the options selected.
Here is some more information about what each of the categories mean:
Compatible
The animals on this list are generally COMPATIBLE with each other and suitable for a saltwater tank volume as indicated. It is still possible for some fish pairings to have occasional chasing, flaring, nipping, swiping or slashing, even between compatible species, but that behavior is likely to be infrequent and non-persistent, not likely to end in significant damage or stress for the fish.
Not Compatible
The animals on this list are generally NOT COMPATIBLE with the option(s) you selected. Trying to care for these animals in the same tank is likely to end badly for one or more of the animals based on aggression or predation. If you were to combine these species in the same tank you could expect to see significant aggression, attacking, bullying, injuring and hiding/fear/stress from the recipient, or even potentially one animal becoming a meal for the other animal. Suffice it to say, this is not a good combination and should be avoided.
Compatible with caution
These animals are considered to be COMPATIBLE WITH CAUTION. You should be cautious about combining these species in the same tank and watch interactions closely to observe for any obvious signs of serious aggression.
While it isn’t an exact science, a way to think about it is that the combination you selected has a certain % chance of working and a certain % chance of not working based on the individual dispositions (almost like personalities) of the animals you acquire. It’s really hard to predict in these instances whether or not it would work, but there are significant numbers of tanks where the combination has worked.
You are taking some risk if you choose to make the pairing, but if you use caution and are prepared to intervene if you see issues, and rescue the animals if they are in danger, you can sometimes make these combinations work.
- Warning signs of trouble: Persistent chasing, torn fins, refusal to eat, excessive hiding, rapid breathing, or visible injuries are signs that aggression is escalating or a fish is stressed.
- What to do if aggression is observed: Rearranging rockwork can break up established territories. Using an acclimation box or divider allows new fish to adjust safely. If aggression continues, temporarily separating the aggressor or the victim may be necessary.
- Have a backup plan: Always be prepared to move a fish to a quarantine tank or rehome it if necessary. Don’t wait for injuries to become severe.
- When to intervene: Occasional chasing or posturing is normal as fish establish hierarchy, but persistent or escalating aggression, refusal to eat, or physical damage means immediate action is needed.
WOULD BE COMPATIBLE BUT THE TANK IS TOO SMALL
These options in yellow under the ‘Compatible’ column with a red ‘i’ warning would be considered COMPATIBLE but the tank size indicated is too small to meet their general care requirements.
It is strongly recommended that you either select different (smaller) fish if you have already committed to the indicated tank size or upgrade the size of your saltwater tank if that is still an option.
Why does tank size matter? Tank size directly affects fish compatibility and welfare. Inadequate space means fish cannot establish territories or escape aggression, leading to chronic stress, stunted growth, and increased disease risk. Smaller tanks also concentrate waste, making water quality harder to maintain. Minimum tank sizes are set to ensure each species has enough room for natural behaviors, both individually and in groups. Ignoring these guidelines often results in aggression, illness, or even death.
WOULD BE COMPATIBLE WITH CAUTION BUT THE TANK IS TOO SMALL
These saltwater fish or corals would be considered COMPATIBLE WITH CAUTION, but the tank size indicated is too small to meet their general care requirements.
It is strongly recommended that you either select different (smaller) fish if you have already committed to the indicated tank size or upgrade the size of your saltwater tank if that is still an option.
Consequences of undersized tanks: When tank size is below recommendations, aggression and stress are amplified, and even “caution” pairings that might succeed in larger tanks often fail. Chronic stress from crowding can suppress immune function and lead to outbreaks of disease.
Why do I see the fish type I entered listed in the results?
Each fish type you enter will also be shown in the results. This is intended to show the relationship between fishes in this category with other fishes within the same category. For example, if you enter “Cardinalfish” into the tool, you will see the result “Cardinalfish” also in the COMPATIBLE results, because you can generally expect groups of cardinalfish to coexist in a community tank.
But if you entered “Tangs/Surgeonfish”, you would see “Tangs/Surgeonfish” in the “Compatible with caution” results, because mixing tangs can be done in the largest tanks, but there are often aggression problems, particularly when the fish are not added together.
Group dynamics and exceptions: Some species, like chromis, anthias, and certain gobies, do best in groups and may become stressed or aggressive if kept singly. Others, such as dottybacks, some wrasses, and many angelfish, are highly territorial and may fight with conspecifics (members of the same species) or similar-looking fish. The success of keeping multiples often depends on group size, sex ratios, and introduction order. For example, keeping a harem of one male and several females is recommended for anthias, while adding all tangs at once (rather than sequentially) can reduce aggression. Always research the social structure of your chosen species before planning groups, and be aware that some exceptions exist where intraspecific aggression is common despite apparent compatibility.
For more information
Check out this Saltwater Aquarium Fish Page to find the care guides for your saltwater fish and learn more about their care requirements. Every care guide generally has descriptions, tank sizes, feeding requirements, additional information about compatibility and some quick facts about the species.
Check out these guides to the best saltwater fish based on the size of your tank:
Each guide will help you see the typical dimensions of each saltwater tank as well as a list of the best fish and a recommendation about how many fish for a tank with that many gallons of water volume.
Common beginner mistakes in saltwater fish compatibility
- Overstocking or impatience: Adding too many fish at once or ignoring compatibility recommendations often leads to aggression and water quality problems.
- Misinterpreting “reef safe”: “Reef safe” means a fish is unlikely to eat corals or invertebrates, but does not guarantee peaceful behavior toward other fish.
- Skipping quarantine: Failing to quarantine new arrivals can introduce disease or parasites, threatening your entire tank.
- Introducing aggressive species first: Adding territorial or aggressive fish before more peaceful species can make it difficult for newcomers to establish themselves.
- Ignoring group dynamics: Not researching whether a species prefers to be kept singly, in pairs, or in groups can lead to stress or fighting.
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