QUICK STATS

Care Level: Easy to Moderate
Diet: Omnivore
Temperament: Peaceful to Mildly Territorial
Reef-Safe: Yes
Source: See Options
Approximate Purchase Size: 1-2"
Approximate Max Size: 3-4"
Recommended Tank Size: 30 Gallons or Larger

BLUE GREEN CHROMIS

The Blue Green Chromis (Chromis viridis) is a classic saltwater aquarium fish known for its shimmering blue-green coloration, active swimming behavior, and peaceful nature. Their color can shift depending on lighting, giving them a bright metallic look that adds movement and sparkle to reef aquariums without demanding the spotlight like some emotionally needy centerpiece fish.

Blue Green Chromis are popular because they are hardy, reef-safe, and usually active in the upper to middle areas of the aquarium. They are often kept in small groups, though aquarists should know that chromis may develop a social hierarchy over time. In plain English: sometimes the group gets along beautifully, and sometimes one chromis starts acting like it owns the lease. Small groups of 3-5 individuals are commonly recommended, with larger tanks helping reduce territorial disputes.

This species does best in aquariums with stable water quality, open swimming space, and enough rockwork for shelter. They make a great choice for reef tanks because they generally leave corals and invertebrates alone, which is the bare minimum we ask of fish and yet somehow still feels worth celebrating.

Note: Image is a representation of what to expect. The fish you receive may vary slightly in size, color, and overall appearance.

AQUARIUM REQUIREMENTS

AQUARIUM SIZE

A minimum tank size of 30 gallons or larger is recommended for a Blue Green Chromis. While a single chromis can do well in smaller established systems, groups will benefit from more swimming room and a larger aquarium. Blue Green Chromis are active mid-water swimmers, so open space in the middle and upper portions of the tank is important.

HABITAT RECOMMENDATIONS

Blue Green Chromis are adaptable, but they do best in stable reef aquariums with both open swimming space and areas for shelter.

Aquascaping: Provide open swimming room along with live rock, caves, and overhangs. This gives them places to retreat when startled or when the group starts holding tiny fish court.

Substrate: Sand or fine aragonite works well and helps create a natural reef-style environment.

Rockwork: Live rock is recommended for shelter and overall biological stability. Chromis may spend much of the day in the water column but still appreciate having somewhere to hide when startled.

Tank Cover: A tight-fitting lid is recommended. They are not the most infamous jumpers, but fish are deeply committed to proving lids matter.

WATER PARAMETERS

Blue Green Chromis are considered hardy, but they still need stable marine conditions. “Hardy” does not mean “immune to chaos,” despite what every beginner aquarium disaster seems determined to test.

Temperature: 75-79°F
pH Level: 8.1-8.4
Salinity: 1.020-1.026 specific gravity
Alkalinity: 8-12 dKH
Ammonia, Nitrite, and Nitrate: Ammonia and nitrite should remain undetectable. Nitrate should be kept as low as reasonably possible, ideally below 20 ppm.
Water Flow: Moderate water movement is ideal. They often enjoy swimming in active water flow, especially in the upper and middle areas of the aquarium.

DIET

Blue Green Chromis are omnivores and should be fed a varied diet that includes both meaty and plant-based foods. In the wild, they feed on planktonic foods and other tiny organisms in the water column, so smaller foods offered throughout the week are ideal.

PRIMARY DIET

Frozen Food: Offer mysis shrimp, enriched brine shrimp, marine blends, and other small frozen foods. Our favorite food for Blue Green Chromis is Reef Frenzy by LRS because it offers a great variety of marine ingredients and usually gets a strong feeding response. Fish eating enthusiastically is helpful, mostly because watching livestock ignore expensive food is one of the hobby’s most disrespectful traditions.

Prepared Foods: High-quality marine pellets or flakes can be offered once the fish are eating reliably. Smaller pellet sizes are best.

Supplemental Foods: Copepods, amphipods, and other small plankton-sized foods can help support natural feeding behavior.

Algae-Based Foods: Spirulina flakes, herbivore blends, or mixed omnivore foods can be included occasionally for variety.

FEEDING FREQUENCY

Feed small amounts 1-2 times per day. In groups, make sure all individuals are getting food and not just the fastest little blue-green missile with a superiority complex.

COMPATIBILITY

Blue Green Chromis are generally peaceful and work well in community reef aquariums. They can be kept singly or in groups, but groups may develop pecking-order behavior over time. Larger tanks and frequent feeding can help reduce stress and aggression.

COMMON TANK MATES

Fish: Clownfish, cardinalfish, gobies, blennies, wrasses, firefish, dwarf angelfish, tangs, and other peaceful to semi-peaceful community fish.

Avoid: Large predatory fish such as lionfish, groupers, large eels, and aggressive fish that may bully or eat them. Tiny peaceful fish do not need to become expensive snacks.

Invertebrates: Blue Green Chromis are safe with most cleaner shrimp, hermit crabs, snails, urchins, and other common reef invertebrates.

Coral: Blue Green Chromis are considered reef-safe and should not bother soft corals, LPS, SPS, zoanthids, mushrooms, or anemones.

BEHAVIORAL NOTES

Temperament: Peaceful overall, though groups can form a hierarchy. Occasional chasing may occur, especially in smaller tanks.

Schooling Behavior: Often sold as a schooling fish, but in aquariums they may behave more like a loose group than a perfect synchronized display. Nature did not consult the marketing department.

Activity Level: Very active and usually visible in the middle to upper water column.

Reef Compatibility: Excellent for reef tanks. They generally ignore coral and invertebrates.

Group Keeping: Small groups of 3-5 are commonly recommended, but long-term success depends on tank size, feeding, and individual behavior. Larger systems tend to offer better results with groups.

Jumping: A tight-fitting lid is recommended. Again, because apparently water is not enough for fish.

ACCLIMATION PROCESS

This acclimation method helps reduce stress by gradually introducing the fish to your aquarium’s temperature and water chemistry.

1. TURN OFF THE LIGHTS & ATO

Turn off aquarium lights to reduce stress. If you have an Auto Top Off system, switch it off before starting acclimation.

2. FLOAT THE BAG

Float the sealed bag in the aquarium for 15-20 minutes to allow the temperature in the bag to equalize with the tank.

3. OPEN BAG, ADD FISH TO CONTAINER

Carefully open the bag and transfer the fish and shipping water into a clean bucket or container.

4. ACCLIMATE USING TANK WATER

Add 1/4 cup of tank water to the container every 5 minutes for 40 minutes.

5. TRANSFER FISH TO AQUARIUM

Once acclimation is complete, use a net or specimen container to gently transfer the fish into the aquarium. Discard the shipping water. Do not pour shipping water into your aquarium.

6. REFILL THE AQUARIUM WITH SALTWATER

You may need to replace the saltwater removed during acclimation with fresh mixed saltwater.