Coralkin honest saltwater & reef care

Livestock · Damsels & Chromis

Green Chromis

Chromis viridis

A shimmering blue-green shoaler — one of the cheapest, hardiest ways to add movement.

Difficulty: Beginner Reef-safe community fish Reef-safe

Illustration of a Green Chromis

The green chromis (Chromis viridis) is a shimmering blue-green shoaling fish — one of the cheapest, hardiest ways to add movement and colour to a reef. Keep them as a group with open swimming space, and know one quirk: over time a “school” often squabbles down to a few, or a pair.

Good to know: Keep an odd-numbered group; they can bully each other down to a pair over time.
📊 What keepers actually ask: The most common green-chromis question is “why is my school disappearing?” — usually in-group aggression, not disease. We cover it up front.

Care at a glance

Adult sizeAbout 3 in (8 cm).
LifespanVery hardy — 8–15 years in a well-run reef.
Minimum tankA 30-gallon (or larger) tank with open mid/top water to swim; keep a group of at least 6.
Temperature75–82°F (24–28°C).
pH8.1–8.4.
Specific gravity1.020–1.026 (≈35 ppt; keep it stable).
Other targetsLow–moderate flow (they're lagoon fish); sensitive to rising ammonia/nitrate — keep the water clean.
DietOmnivore — small meaty frozen foods, marine flake/pellet, and some greens; several small meals a day.
TemperamentPeaceful with tankmates and beginner-friendly — but within their own group they set a pecking order and can bully each other down over time.
Reef-safeYes — reef-safe; won't nip corals (they pick plankton and algae from the water).
Natural rangeIndo-Pacific lagoons and reef flats.
Beginner-friendly, done right. About as hardy and cheap as marine fish get — a classic first shoaling fish. Two honest caveats: keep a real group (6+) with swimming room, and expect some in-group squabbling that can whittle the numbers down. They also dislike dirty water, so they reward a stable tank.
What does a green chromis really cost? The green chromis itself is usually the cheapest part — the reef system is the real cost. See the honest green chromis cost breakdown (upfront vs ongoing, and where it's safe to save). No prices quoted.
Planning your stock list? Before you buy, run your tank and wish-list through our free stocking & tank-size calculator — it checks this fish's minimum tank and shoal size and flags any aggression clash, so you don't overstock.

The fish store gets these wrong

Common myths, kindly corrected — no shame for having believed them.

  • “A big school will stay a big school.” Often not — green chromis set up a pecking order and can bully each other down to a few, or a pair, over months. Start with a solid group (6+) and give them space.
  • “They're indestructible.” Hardy, yes — but they're sensitive to rising ammonia and nitrate. A stable, cycled tank matters.

Before you buy

  • Buy a group of at least 6 for the best odds of a stable shoal.
  • Give them open swimming water and low–moderate flow.
  • Keep nutrients in check — they don't love dirty water.
  • Add the group together, not one at a time.

Quarantine and get help if…

We can't diagnose from a photo — but these are the signs to stop watching, quarantine, and get an aquatic vet or an experienced reefer's eyes on it:

  • White salt-grain spots, flashing, or rapid gill-breathing (possible ich or velvet).
  • Cloudy skin patches, clamped fins, or gasping at the surface.
  • One being chased relentlessly and refusing food, or a hollow belly.
  • Any new fish added without quarantine.

Print the Green Chromis emergency vet-prep card — what to bring, what to tell the vet, and the questions to ask.

Never

  • Never keep a single green chromis expecting shoaling behaviour — buy a group.
  • Never let nitrates climb — they're sensitive to it.
  • Never add them to an uncycled tank.

Common green chromis questions

How many green chromis should I keep together?

A group of at least 6, added together, with open swimming space. Larger groups fare best — but expect some in-group squabbling as they set a pecking order.

Why is my green chromis school shrinking?

Usually in-group aggression, not disease. Green chromis establish a hierarchy and can bully weaker members down over months, often ending at a pair. A bigger group and more swimming space reduce it.

Are green chromis reef-safe?

Yes — they won't nip corals. They pick plankton and algae from the water and are a classic peaceful reef shoaler.

How long do green chromis live?

They're very hardy — 8–15 years is possible in a well-maintained reef with clean, stable water.

What do green chromis eat?

Omnivores — small meaty frozen foods, marine flake or pellet, and some greens, fed as several small meals a day.

🐚 Did you know? — Green Chromis fun facts

Little true delights about the green chromis — each one checked against a named source, no reef-store folklore.

  • Green chromis gather in shimmering schools around Acropora coral heads, a living cloud of apple-green above the branches. Wikipedia
  • When a male green chromis is ready to breed he turns a warmer yellow, builds a nest on the sand, then guards the eggs and fans them with his fins. Wikipedia
  • A guarding male green chromis will eat any eggs that fail to hatch, keeping the nest clean of microbes that could threaten the rest of the clutch. Wikipedia

More reef fun facts →

Sources & further reading

This guide was written and fact-checked against these authorities. It's honest, general guidance — not a diagnosis, and not a substitute for an aquatic vet or your own test kit:

Written and fact-checked by The Coralkin Team against marine-aquarist and veterinary sources — if your green chromis shows a red-flag sign above, quarantine and get an aquatic vet or an experienced reefer's eyes on it. We never guess a care number.

🔬 Review status: team-written and fact-checked against cited sources · not yet reviewed by a marine vet. How we research & fact-check →

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