Blue Green Chromis (Green Chromis)

1) Where they come from

Blue Green Chromis (Chromis viridis) are little reef fish from the Indo-Pacific—think shallow lagoons and reef slopes where they hang in groups above branching corals. That “sparkly blue-green” look makes more sense when you picture them hovering in sunlight over acropora.

2) Setting up their tank

These are beginner-friendly, but they do best when you set them up like a calm, open-water corner of a reef: plenty of swimming room with rockwork they can duck into. They’re not the kind of fish you buy for a tiny tank and hope for the best.

• Tank size: I’d start at 20–30 gallons for a small group, bigger is easier if you want 5–7+
• Aquascape: rock structure with caves/branches + open water in front for schooling
• Flow/oxygen: moderate flow and good surface agitation—chromis like clean, oxygen-rich water
• Lighting: whatever your reef has; they don’t care as long as they have cover
• Parameters to aim for: 1.025ish salinity, 76–79°F, stable pH/alk—steady beats chasing numbers

3) What to feed them

Chromis are easy eaters once they’re settled. In the wild they pick zooplankton out of the water column all day, so think small foods and frequent-ish feeding. Mine always did better on two smaller meals than one big dump of food.

• Staples: quality marine pellets and small marine flakes (they’ll take them readily)
• Frozen: mysis, brine (better as a treat), finely chopped krill, roe/eggs blends
• Tiny stuff they love: copepods, cyclops, small plankton foods
• Feeding pattern: 1–2x/day in most home tanks; 2–3x/day if you’re trying to fatten up skinny new arrivals (watch nutrients)

4) Behavior and tankmates

They’re “peaceful” in the sense that they won’t terrorize your tank, but they do have a pecking order. In a roomy tank they hover, flash that neon color, and move as a group. In cramped setups, the bossy one can make life miserable for the weakest fish.

• Good tankmates: clownfish, gobies, blennies, peaceful wrasses, firefish (with enough hiding spots), tangs in larger tanks
• Avoid: very aggressive dottybacks, big mean damsels, hawkfish that like to bully, and anything that sees them as snacks
• Reef safety: they’re reef-safe and ignore corals/inverts

5) Breeding tips (if you want to try)

They can spawn in home tanks, especially if you keep a small group well-fed in a stable reef. Spawning usually looks like one fish getting extra territorial over a spot (often a rock face), cleaning it, then doing quick little chase-and-display routines.

• What they lay: adhesive eggs on a cleaned patch of rock
• Who guards: the male typically stays close and fans the eggs
• If you want fry: you’ll need a separate larval setup—newly hatched larvae are tiny and need live foods like rotifers, then baby brine later

6) Common problems to watch for

Most chromis issues come from three things: stress from shipping/pecking order, parasites, and infections that show up after a week or two. They can look perfect on day one and then start dropping off one-by-one if you ignore early warning signs.

• Uronema-like symptoms: red sores, frayed areas, rapid decline (more common in chromis than many reef fish)
• Ich/velvet: flashing, heavy breathing, staying in high flow, white dusting or spots
• Starvation/being outcompeted: skinny belly, hanging back at feeding time
• Bullying within the group: one fish constantly chased, hiding, fins getting ragged