Adrian Pingstone · Public domain — Wikimedia Commons (cropped)
Green Chromis
Chromis viridis
Active blue-green shoaler for a peaceful reefBeginner
- Lifespan
- 8-15 years
- Size
- 8-10 cm (3-4 in)
- Social needs
- Shoaling; keep an odd-numbered group
- Time
- Daily feeding; weekly testing/changes
- Cost
- Medium
- Diet
- Omnivore (mysis, brine, marine flake/pellet)
Overview
What is this animal?
- The Green Chromis is an iridescent blue-green damselfish that schools in the open water of a reef.
- Hardy, inexpensive, and active, it adds constant movement, and unlike most damsels it is relatively peaceful, which makes it a reasonable beginner shoaling species.
- They are among the tougher marine fish available and tolerate minor beginner mistakes within a cycled tank.
- A well-fed group moving in unison across the tank is a striking display.
Temperament
- Peaceful by damselfish standards and reef-safe, Green Chromis school together in open water and ignore corals.
- However, as they mature a hierarchy forms and dominant fish often pick off subordinates one by one until only one or two remain.
- Counter this by stocking an odd-numbered group of five or more at once in a roomy tank.
- They mix well with other peaceful community fish and add coordinated open-water movement.
A good fit for
- Beginners wanting an active group
- Larger reef and FOWLR tanks
- Keepers on a tighter livestock budget
- Adding open-water movement
Common mistakes to avoid
- Buying too few - they cull down to one
- Adding them piecemeal instead of together
- Undersized tank for an active school
- Aggression as the group matures
Enclosure
Minimum 110 litres (29 US gallons) — for a group of 3
Cannot be kept alone. The minimum is 3, and the space above is for that group.
- Keep a group in a cycled tank of 110L (30 gal) minimum, with larger volumes strongly preferred so the school has swimming room.
- Maintain salinity 1.024-1.026, temperature 24-27°C (75-80°F), pH 8.1-8.4, and nitrate low, with the moderate-to-strong flow they prefer.
- Provide open swimming space plus live rock for refuge.
- A larger tank and bigger group help spread out the aggression that develops as they mature and keep the schooling behaviour intact over the long term.
Supplies
Setup
- Tank, stand and sump
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Marine flake or small pellet
- Frozen mysis shrimp
- Frozen brine shrimp
- Frozen cyclops or copepods
- Algae-based marine food
- Small thawing cup and strainer
- Turkey baster for spreading food in the current
Safe substrate: Aragonite sand · Dry or cured live rock · Bare bottom
Care routine
Daily
- Check salinity, temperature and flow
- Feed
- Head-count and look everyone over
- Top up evaporation with fresh water
Weekly
- Service the skimmer and filter socksevery 3 days
- Clean the glass
- Count the group
- Test the water
Monthly
- Water changeevery 2 weeks
- Calibrate the refractometer
- Check salt, RO/DI and reagents
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Vet: Quarterly group and aggression review — every 3 months
Top resources for more info
Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-09-19.
YouTubers
Sites
Go deeper
Diet
- Green Chromis are omnivores.
- Offer a marine flake or pellet staple plus frozen mysis and brine shrimp, fed once or twice daily.
- In the wild they pick zooplankton from the water column, so they appreciate small foods that drift in the current.
- They feed eagerly and rarely need coaxing, which makes them easy to keep well-fed in a busy tank.
- A varied diet maintains their blue-green sheen and supports the group's condition and activity.
Health
- Chromis are hardy and disease-resistant, tolerating minor parameter swings better than most marine fish.
- The main issue is stress-driven aggression within the group, which can lead to injuries, bacterial infections, and a dwindling school.
- Quarantine new fish and keep nitrate low; marine ich is the usual risk after poor quarantine.
- Watch for nipped fins and isolated, hiding individuals as signs of in-group bullying.
- A large enough group and tank keeps stress and disease low.
Is your enclosure big enough?
Is this urgent?
In a reef, stability matters more than any single target number. A parameter moving fast does more damage than a parameter sitting slightly off.
Go now
Today
Quarantine every new animal, including corals and inverts. It is the single practice that separates a reef that lasts from a reef that restarts.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Bedding and substrate
In a marine system the rock and the sand are life support, and how you start them decides the first six months.
Safe
With a caveat
Never
This is our general list for saltwater fish. We have not built one specific to Damselfish yet.
My kit says 0.25 ppm. Is that dangerous?
A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.
Compare with other animals
The same axes for every animal, side by side — the way the guides are written makes that a fair comparison rather than two articles.
Damselfish, side by side
Same axes, same care guides — the honest way to choose between types.
See all Damselfish side by side →
