Saltwater fish compatibility chart: 22 popular fish, every pair checked

The chart

Read across a row and down a column: ✕ is a problem (the pair doesn't work as a rule), ! is a caution (possible, with conditions), and a blank cell means none of the checks found a conflict. Numbers match the fish list in the first column. Hover over a mark for the reason; the fish-by-fish list below spells out every one.

The four rules behind it

1. One clownfish species

LiveAquaria lists the maroon clownfish's temperament as aggressive and says it is aggressive toward other clownfish; it lists the clarkii as semi-aggressive. Our rule is the conservative one: one species per tank, kept singly or as a pair. Every mixed-species clownfish pair on the chart is a problem.

2. One tang, unless the tank is very large

LiveAquaria says the powder blue tang is extremely aggressive toward other tangs and should be the only one in the tank except in very large systems, and that the tomini is aggressive toward other tangs but peaceful with other fish. Quality Marine adds that Acanthurus tangs are known to be aggressive toward similarly shaped tangs. The chart marks tang pairs as cautions because it assumes a 500 gallon tank; in a tank under 180 gallons, our cut-off for "very large", the stocking calculator treats any second tang as a problem. If you do mix tangs, add them at the same time.

3. Nothing small enough to eat

LiveAquaria says the longnose hawkfish eats small fish and shrimp. The cut-off is ours: the chart flags any tankmate that is 3 inches or smaller as an adult. Among the fish here, that catches the royal gramma, firefish goby, mandarin dragonet, six-line wrasse and Banggai cardinalfish.

4. Watch the midas blenny with gobies

LiveAquaria rates the midas blenny peaceful and reef compatible, but says it sometimes vexes small planktivores and has been known to nip at firefish and gobies, mostly in confined tanks. Those pairs are cautions, not problems.

Tank mates to avoid, fish by fish

The same results, read one fish at a time. Each name links to its care sheet or tank-size page.

• Ocellaris clownfish: avoid Clark's clownfish (two clownfish species); avoid maroon clownfish (two clownfish species).
• Yellow tang: caution with blue tang (two tangs); caution with powder blue tang (two tangs); caution with tomini tang (two tangs).
• Royal gramma: avoid longnose hawkfish (predator and prey).
• Firefish goby: avoid longnose hawkfish (predator and prey); caution with Midas blenny (the blenny may nip).
• Mandarin dragonet: avoid longnose hawkfish (predator and prey).
• Flame angelfish: no conflicts with the other fish on the chart.
• Six-line wrasse: avoid longnose hawkfish (predator and prey).
• Clark's clownfish: avoid ocellaris clownfish (two clownfish species); avoid maroon clownfish (two clownfish species).
• Maroon clownfish: avoid ocellaris clownfish (two clownfish species); avoid Clark's clownfish (two clownfish species).
• Blue tang: caution with yellow tang (two tangs); caution with powder blue tang (two tangs); caution with tomini tang (two tangs).
• Powder blue tang: caution with yellow tang (two tangs); caution with blue tang (two tangs); caution with tomini tang (two tangs).
• Foxface rabbitfish: no conflicts with the other fish on the chart.
• Green chromis: no conflicts with the other fish on the chart.
• Banggai cardinalfish: avoid longnose hawkfish (predator and prey).
• Longnose hawkfish: avoid royal gramma (predator and prey); avoid firefish goby (predator and prey); avoid mandarin dragonet (predator and prey); avoid six-line wrasse (predator and prey); avoid Banggai cardinalfish (predator and prey).
• Yellow watchman goby: caution with Midas blenny (the blenny may nip).
• Diamond goby: caution with Midas blenny (the blenny may nip).
• Tomini tang: caution with yellow tang (two tangs); caution with blue tang (two tangs); caution with powder blue tang (two tangs).
• Copperband butterflyfish: no conflicts with the other fish on the chart.
• Melanurus wrasse: no conflicts with the other fish on the chart.
• Midas blenny: caution with firefish goby (the blenny may nip); caution with yellow watchman goby (the blenny may nip); caution with diamond goby (the blenny may nip).
• Lawnmower blenny: no conflicts with the other fish on the chart.

Fish with conditions of their own

Some fish raise a flag whatever they share the tank with. These come from the stocking calculator's species notes:

• Mandarin dragonet: needs a well-established tank (LiveAquaria) with a thriving pod population (Bulk Reef Supply). Unless it is captive-bred and already eating frozen food, don't add it to a new tank.
• Flame angelfish: LiveAquaria says it should be the last fish added to a peaceful community, in an established system, and may nip corals and clam mantles.
• Six-line wrasse: bullies fish added after it, especially in small tanks, so add it last.
• Diamond goby: LiveAquaria recommends live sand and an attached, populated refugium, and frequent feeding.
• Copperband butterflyfish: LiveAquaria rates it difficult to feed; confirm it is eating in quarantine before adding it.

What the chart doesn't check

• Tank size. The chart assumes a tank big enough for any pair. Your tank may not be: a powder blue tang and a firefish don't conflict, but only one of them fits a 20 gallon. The stocking calculator checks a whole list against your tank's volume and footprint.
• Corals and invertebrates. Compatibility here is fish against fish. For corals, shrimp and clams, see the reef-safe fish list.
• Individuals and order. Fish vary, and the order you add them matters: the calculator's own notes say to add the six-line wrasse and the flame angelfish last.
• Disease. The most compatible pair still fails if one arrives with ich; new fish go through a quarantine tank first.