Green Chromis Care Guide: Tank Size, Diet, Schooling & Tankmates
Green Chromis care made simple: tank size, diet, how many to keep in a school, reef-safe tankmates, health tips, and what to look for when buying.
The Green Chromis (Chromis viridis) is a small, peaceful schooling fish with a shiny blue-green body. A group of them swimming together adds movement and color to almost any reef tank.
Quick facts
- Tank size: 30 gallons for a small group; 55+ for 5 or more
- Adult size: about 3 to 4 inches
- Diet: omnivore; mysis, brine shrimp, pellets, and flakes
- Reef safe: yes, ignores corals and inverts
- Difficulty: easy
- Temperament: peaceful, but squabbles inside its own group
Why reefers love it
Green Chromis spend the day in open water instead of hiding. That makes them one of the easiest ways to bring a tank to life.
They are also cheap, hardy once settled, and safe with corals, clams, shrimp, and snails.
Green or Blue Reef Chromis?
Stores often sell two look-alikes. The Green Chromis is pale blue-green and shimmers under light.
The Blue Reef Chromis (Chromis cyanea) is a deeper royal blue with a black edge on the tail. Both need the same basic care, but check the label so you know what you are buying.
Tank setup
- Swimming room: leave open water in front of the rockwork
- Hiding spots: branching rock or coral for them to dart into at night
- Water: 74–79°F, salinity 1.023–1.026, pH 8.1–8.4
- Lid: recommended, since chromis can jump when spooked
Keeping a school
Chromis feel safest in groups, but a group comes with a pecking order. The biggest fish may chase the smallest one.
- Buy 3, 5, or 7 fish and add them all at the same time
- Give a bigger tank to bigger groups so the weakest fish can get away
- Expect a group to shrink over time in small tanks; this is normal
Diet and feeding
In the wild they pick tiny food out of the water. In a tank they eat almost anything that floats by.
- Frozen mysis or enriched brine shrimp
- Small marine pellets or flakes
- A pinch of nori or algae food now and then
- Feed small amounts 2 to 3 times a day
Frequent small meals keep them plump and help cut down on fighting.
Tankmates
- Good matches: clownfish, gobies, blennies, royal grammas, cardinalfish, and tangs
- Use caution: dottybacks and damsels that guard territory
- Avoid: lionfish, groupers, and other fish big enough to eat them
Photo: Debra Baker, Wikimedia Commons, CC BY 4.0 — wild Green Chromis in Kiribati
Health tips
Most Green Chromis are wild caught, so the first few weeks matter most.
- Quarantine: keep new fish in a separate tank for a few weeks first
- Watch for: white spots, fast breathing, or red sores, which can mean a parasite or infection
- Stable water: do small, regular water changes and test often
Once settled, a healthy chromis can live 5 to 10 years or more.
Buying tips
- Look for: bright color, clear eyes, and fish that swim with the group
- Skip: fish that hide alone, look thin, or breathe fast
- Ask: to see them eat before you take them home
Planning a peaceful community? Read our Royal Gramma guide next.
FAQ
How many Green Chromis should I keep? Start with 3 or 5 added at once. In tanks under 55 gallons, 3 is usually the safest number.
Can I keep just one Green Chromis? Yes. A single chromis is fine, but it may hide more than a fish in a group.
Why are my chromis disappearing? Usually it is bullying inside the group or a disease after shipping. Bigger tanks, quarantine, and frequent feeding help.
Ready to start a school? Browse livestock and gear in the ReefBay shop, then track feedings and water tests in the ReefBay app.
