Green Chromis

Chromis viridis

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

Difficulty: BeginnerReef-safe community fishReef-safe

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 size	About 3 in (8 cm).
Lifespan	Very hardy — 8–15 years in a well-run reef.
Minimum tank	A 30-gallon (or larger) tank with open mid/top water to swim; keep a group of at least 6.
Temperature	75–82°F (24–28°C).
pH	8.1–8.4.
Specific gravity	1.020–1.026 (≈35 ppt; keep it stable).
Other targets	Low–moderate flow (they're lagoon fish); sensitive to rising ammonia/nitrate — keep the water clean.
Diet	Omnivore — small meaty frozen foods, marine flake/pellet, and some greens; several small meals a day.
Temperament	Peaceful with tankmates and beginner-friendly — but within their own group they set a pecking order and can bully each other down over time.
Reef-safe	Yes — reef-safe; won't nip corals (they pick plankton and algae from the water).
Natural range	Indo-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.

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.

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.

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:

Saltwater Aquarium Blog — Green Chromis Care Guide — adult size, lifespan, group size, tank, temperament, reef-safe, water sensitivity, diet

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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