---
type: species
title: "Koran Angelfish Care Guide: The Semicircle Angel for Large Reefs"
slug: "koran-angelfish"
category: "saltwater"
scientificName: "Pomacanthus semicirculatus"
subcategory: "Large Angelfish"
lastUpdated: "2026-04-26"
readingTime: 10
url: https://www.fishstores.org/species/koran-angelfish
---

# Koran Angelfish Care Guide: The Semicircle Angel for Large Reefs

*Pomacanthus semicirculatus*

Master Koran Angelfish care. Learn about the stunning Pomacanthus semicirculatus transformation, tank mate compatibility, and reef-safe status.

## Species Overview

The koran angelfish (*Pomacanthus semicirculatus*) is one of the most dramatic transformation stories in the marine hobby. The fish you buy at four inches — a midnight-blue oval crossed by electric white and powder-blue semicircles — looks nothing like the fish you will own three years later. The adult sheds the juvenile pattern entirely and emerges as a yellow-green swimmer covered in iridescent blue spots and looping markings that early naturalists thought resembled Arabic calligraphy. That visual reference is where both the common name "koran" and the species' scientific epithet *semicirculatus* (referring to the juvenile's semicircular bands) come from.

For intermediate to advanced reefers, the koran sits in a peculiar slot. It is not a beginner fish — the tank size, the feeding requirements, and the disease sensitivities all push it firmly into the "you should already know what you're doing" category. But it is also not as fragile as some of the rarer large angels. With the right system and a thoughtful quarantine, a koran will live 15 to 20 years and reach roughly 15 inches, becoming the unmistakable centerpiece of a fish-only or FOWLR display.

| Field       | Value                 |
| ----------- | --------------------- |
| Adult size  | 12-15 in (30-38 cm)   |
| Lifespan    | 15-20 years           |
| Min tank    | 250 gallons           |
| Temperament | Semi-aggressive       |
| Difficulty  | Intermediate-Advanced |
| Reef safe   | With caution          |

### The Dramatic Transformation: Juvenile vs. Adult Patterns

Juvenile korans are arguably more striking than the adults. A two- to four-inch juvenile is deep navy blue, almost black, marked by sharp white and electric-blue concentric semicircles that radiate from the tail. The pattern is so vivid that newcomers often mistake juveniles for a completely different species — a confusion compounded by the fact that the juvenile koran looks nearly identical to the juvenile blueface (*Pomacanthus xanthometopon*) and emperor angelfish at the smallest sizes.

The transition begins around five to six inches and is one of the longest, most gradual color changes of any reef fish. The semicircle bands start to fragment near the tail, the body color shifts from black-blue toward greenish-yellow, and small blue spots begin to dot the flanks. By eight inches, you are looking at a hybrid pattern — half juvenile, half adult — that some hobbyists actually find unattractive compared to either end state. By 10 inches the transformation is essentially complete: a yellow-green body, pale yellow caudal fin, and the famous looping blue script across the head and operculum.

This entire metamorphosis takes 18 to 36 months depending on growth rate, diet, and tank size. A koran in a 180-gallon tank will transition slower than one in a 400-gallon system simply because crowding suppresses growth. There is no way to stop or reverse the change — it is hormonal and inevitable — so go in knowing that the fish you buy is not the fish you will keep.

> **Juvenile to adult transition timeline**
>
> Roughly: 2-4 inches is full juvenile pattern, 5-7 inches is early transition with bands fragmenting, 7-10 inches is "ugly duckling" phase with mixed coloration, and 10-15 inches is full adult. Plan for 24 months of slow change. Photograph monthly — the gradual shift is hard to notice day-to-day.

### Natural Habitat: Indo-Pacific Reefs and Lagoons

Korans range across one of the widest distributions of any angelfish, from the East African coast and the Red Sea east through the Maldives, the entire Indo-Australian archipelago, the Great Barrier Reef, and north to southern Japan. They favor sheltered lagoon reefs, seaward slopes, and coral-rich rubble zones at depths of roughly 5 to 130 feet. Juveniles are usually found in shallow, protected areas — often inside crevices in dead coral or among rubble — while adults move to deeper, more open sections of the reef.

In the wild they are solitary or paired, never schooling. They graze constantly across live rock for sponges, tunicates, and macroalgae, and they cover surprising distances in a day. That ranging behavior is exactly why captive specimens demand so much swimming volume — a koran confined to a 125-gallon cube spends months pacing the same six-foot stretch of glass, which is one of the most reliable triggers for HLLE and stress-related disease.

### Size and Lifespan: 15 Inches and Two Decades

A wild *Pomacanthus semicirculatus* tops out at around 16 inches; captive specimens usually settle between 12 and 15 inches in tanks of 250 to 400 gallons. Properly fed and housed, a koran should live 15 to 20 years — comparable to the [emperor angelfish](/species/emperor-angelfish) and [french angelfish](/species/french-angelfish), and considerably longer than most reef fish. That lifespan is one of the strongest arguments for not buying one casually. You are signing up for a fish that may outlive your current tank, your current career, and possibly the room it lives in.

## Water Parameters & Tank Requirements

Korans are tougher than people give them credit for once acclimated, but they are not forgiving of swings. Stable parameters matter more than chasing perfect numbers, and the bigger the system, the easier stability becomes.

### Minimum Tank Size: 250 Gallons for Adults

A 250-gallon, six-foot tank is the realistic minimum for a single adult koran. Smaller systems — 180 gallons and below — are viable only as grow-out tanks for juveniles you genuinely plan to upgrade within a year or two. Stuffing a full-grown 14-inch angel into a four-foot 125-gallon tank is the marine equivalent of keeping a goldfish in a bowl: the fish will live, but its growth will stunt, its color will fade, and its lateral-line erosion will be on the schedule.

If you can build to 300 or 400 gallons, do it. Korans are visibly more relaxed and more colorful in larger volumes, and the added water buffer dramatically reduces the workload on your protein skimmer and your patience.

| Parameter         | Target                  | Notes                          |
| ----------------- | ----------------------- | ------------------------------ |
| Temperature       | 72-78 degF (22-26 degC) | Stable matters more than exact |
| pH                | 8.1-8.4                 | Match natural seawater         |
| Specific gravity  | 1.020-1.025             | 1.025 for FOWLR, 1.026 if reef |
| Ammonia / Nitrite | 0 ppm                   | Non-negotiable                 |
| Nitrate           | Under 20 ppm            | Korans dislike high NO3        |
| Min tank size     | 250 gallons             | 300+ strongly preferred        |
| Flow              | Moderate to high        | 20-40x turnover                |

### Specific Parameters: 72-78 degF, pH 8.1-8.4, SG 1.020-1.025

Aim for the middle of every range. Temperature at 76 degF, pH at 8.2, specific gravity at 1.025 for fish-only systems or 1.026 if you are running corals. The koran will tolerate brief excursions outside these bands, but rapid swings — a 4-degree drop overnight from a failed heater, a 0.3 pH swing from a CO2-loaded room — are how stress turns into disease. Calibrate your refractometer with reference solution monthly; an uncalibrated swing-arm hydrometer is one of the most common silent killers of large angels.

### Filtration and Flow: High-Oxygen Environments and Protein Skimming

Large angels are oxygen pigs. They are big-bodied, active swimmers with high metabolic demand, and they live in well-flushed reef zones where dissolved oxygen sits near saturation. A koran in a tank with marginal aeration will breathe heavily at the surface within hours. Plan for redundant flow: at least one large internal powerhead in addition to the return pump, plus a sump with high gas exchange.

A protein skimmer rated for at least 1.5x your display volume is mandatory, not optional. Korans produce dense, high-protein waste from their meat-and-sponge diet, and a marginal skimmer leaves nitrates climbing fast. Refugium macroalgae help on the back end, and a quality filter sock or roller filter in the sump catches the inevitable particulate from grazing on rock.

> **Do not skimp on the skimmer**
>
> Korans push tank chemistry hard. A budget skimmer that "just barely" handles your display under normal stocking will be overwhelmed within months of adding a 10-inch angel. Oversize the skimmer by at least 50 percent of the manufacturer's recommended volume rating, and clean the neck weekly.

## Diet & Feeding

Diet is the single biggest reason captive korans fail in their first year. The species is a true spongivore in the wild, and replicating that nutrition profile in captivity takes more than dropping flake into the tank.

### Spongivore Requirements: The Importance of Specialized Angel Formulas

In the wild, sponges and tunicates make up an enormous share of a koran's diet — animals that contain unusual lipids and fatty acids most aquarium foods do not provide. Without a sponge-based component, captive korans slowly develop nutritional deficiencies that show up as faded color, lethargy, and accelerated HLLE.

Build the diet around a frozen "angelfish formula" containing actual sponge matter. Brands like Ocean Nutrition Angel Formula, LRS Reef Frenzy, and Rod's Food Angel Blend all incorporate marine sponge and the right lipids. Feed this product as the staple — once or twice daily — and rotate in supplemental items rather than the other way around.

### Grazing Habits: Providing Ample Live Rock for Foraging

Korans graze constantly. In a healthy display, you should see the fish pick at live rock between scheduled feedings — nipping at film algae, copepods, sponge fragments, and the occasional tunicate. A tank with sparse rockwork forces the koran to depend entirely on hand-feeding, which both increases stress and shortcuts the slow grazing behavior that helps wear down their continuously growing teeth.

Aim for 1 to 1.5 pounds of mature live rock per gallon of display, arranged in open structures with multiple swim-throughs rather than a solid wall. The fish wants horizontal cruising lanes broken by overhangs and caves, not a hill it has to circle.

### Supplementation: Vitamin-Enriched Mysis and Nori Sheets

Round out the staple angel formula with three supplemental categories:

- **Mysis and krill** soaked in a vitamin supplement like Selcon or Vita-Chem twice a week. The added HUFAs and Vitamin C protect against HLLE.
- **Nori sheets** clipped to the glass daily. Korans pick at green and red nori between meals, and the iodine in nori supports thyroid function.
- **Pellets** as backup. A high-quality marine pellet (New Life Spectrum Marine Formula, Hikari Marine S) keeps a baseline going on travel days. Korans are typically eager pellet eaters once acclimated.

Feed two to three times daily in smaller portions rather than one large meal. A grazer's stomach is small relative to its body, and big single feedings push waste through the system faster than the skimmer can keep up.

## Tank Mates & Compatibility

Large angels are semi-aggressive ambassadors of their own social rules. The koran is moderate by *Pomacanthus* standards — less psychotic than a [queen angelfish](/species/queen-angelfish), more dominant than a [coral beauty](/species/coral-beauty-angelfish) — but you still need to plan stocking carefully.

### Reef Safe? Caution: Picking on LPS, Zoanthids, and Clams

The honest answer to "is the koran reef safe" is "no, but maybe." In a large, well-fed system with primarily SPS corals and no clams or zoanthids, many korans coexist with the reef for years. Drop the same fish into a mixed reef heavy with hammers, frogspawn, scolymia, and clams, and you will lose coral tissue weekly.

The pattern is consistent across the *Pomacanthus* genus: SPS corals are usually safe, mushrooms and most leathers are usually safe, but LPS polyps, zoanthid colonies, and tridacnid clam mantles get nipped. Tunicate-heavy aquacultured rock will also get demolished. If your reef investment matters more than the angelfish, pick a different fish. If the angel is the centerpiece and you treat coral as decoration, accept the risk and stock accordingly.

> **Adding the koran to an established reef tank**
>
> The most common heartbreak with this species: a hobbyist with a thriving five-year reef adds a koran "just to try it." Within two weeks, the LPS look chewed, the clam closes permanently, and the zoa garden is bald. By the time the fish is rehomed, the damage is done. If you want a koran, design the system around the fish from day one, or commit to a fish-only display.

### Managing Intraspecific Aggression: Keeping Only One Pomacanthus

One koran per tank. One *Pomacanthus* per tank, ideally, unless you are running a 1,000-gallon-plus system with deliberate planning. Korans recognize their own species' silhouette and will fight to the death if forced to share territory. The same goes for similar-bodied congenerics — a koran and an emperor angelfish in the same 250 will end with one of them dead or hiding permanently.

If you are determined to mix multiple large angels, the only reliable approach is to add all specimens simultaneously as small juveniles to an oversized tank and accept that you may still need to rehome one as they mature. Even then, expect chasing during the transition period when their adult patterns emerge.

### Suitable Large Semi-Aggressive Companions

Korans coexist well with other big-personality reef fish that occupy different niches:

- **Tangs** — a [yellow tang](/species/yellow-tang), [naso tang](/species/naso-tang), or [purple tang](/species/purple-tang) for grazer diversity
- **Triggerfish** — [niger triggerfish](/species/niger-triggerfish) and [picasso triggerfish](/species/picasso-triggerfish) work well; avoid the meaner clown trigger
- **Wrasses** — large [melanurus wrasse](/species/melanurus-wrasse), [six-line wrasse](/species/six-line-wrasse), or fairy wrasses for color and pest control
- **Groupers and basses** — chalk bass and small grouper species
- **Schooling support** — [banggai cardinalfish](/species/banggai-cardinalfish) or anthias if your tank can support a shoal

Avoid timid or slow-eating species that will starve at feeding time — pipefish, mandarins, small dragonets, and slow-moving butterflyfish — and avoid any same-shape angelfish.

## Common Health Issues

Large angels get sick. Korans specifically have a reputation for being magnets for two ich-family parasites and slow-burning lateral-line erosion. A proper quarantine and a stable system prevent most of it.

### Marine Ich (Cryptocaryon irritans) and Velvet

Marine ich (*Cryptocaryon irritans*) and the more lethal marine velvet (*Amyloodinium ocellatum*) are both dinoflagellate-style parasites that thrive in large angels. Korans seem especially prone, possibly because of the stress associated with shipping and acclimation at the size most are sold. White spots, scratching against rock, rapid gill movement, and clamped fins are the early signs.

Standard treatment is copper sulfate at therapeutic levels (0.30 to 0.50 ppm of free copper) in a dedicated quarantine tank for 30 days, or tank transfer method for ich specifically. Velvet moves fast — a fish showing heavy breathing in the morning can be dead by evening — so quarantine is non-emotional preventative work, not a "wait and see" decision.

### Lateral Line Erosion (HLLE) in Large Angels

Head and lateral line erosion (HLLE) is a slow, ugly disease that pits the head and lateral line of large angels and tangs over months. The exact cause is debated, but the consensus risk factors are well established: poor diet (especially missing HUFAs and Vitamin C), high nitrates, stray voltage in the tank, and chronic stress from undersized systems.

Prevention: vitamin-soaked mysis weekly, nori clips daily, nitrates under 20 ppm, a grounding probe in the sump, and an appropriately sized tank. Reversal is possible but slow — expect six to twelve months of recovery once the underlying cause is fixed. New tissue grows back lighter than the surrounding skin and may never fully blend.

### Copper Sensitivity During Quarantine

Korans are moderately copper-sensitive at the dosages used to treat ich. Start at the low end of the therapeutic range (0.20 to 0.25 ppm) and ramp slowly to 0.30 ppm over 48 hours rather than slamming the fish with full-dose copper on day one. Watch for darkened color, refusal to eat, and rapid gill ventilation — all signs the fish is toxified rather than parasitized.

If your koran tolerates copper poorly, switch to chloroquine phosphate (CP) at 60 mg/gal as the second-line treatment. CP is gentler on angels and treats both ich and velvet, but it is harder to source and tougher on filter biology.

> **Quarantine every large angel for 30 days minimum**
>
> No exceptions. The cost of a 40-gallon QT tank, a heater, and a sponge filter is a fraction of the cost of a $200 koran, and the cost of treating an ich outbreak in your 300-gallon display is incalculable. Always quarantine. Use copper or CP prophylactically if the fish came through a wholesaler.

## Where to Buy & What to Look For

Korans are usually sold as juveniles in the 2 to 4 inch range, occasionally as sub-adults at 5 to 7 inches. Adults are rarely traded because of shipping difficulty and the price they command. The sweet spot for a buyer is a healthy 3 to 4 inch juvenile that has had time to settle at the wholesaler or store.

### Selecting a Healthy Juvenile: Alertness and "Pinching"

A healthy juvenile koran swims confidently in open water, holds its fins fully extended, and reacts to your presence near the glass. Color should be deep midnight blue with sharp, bright white and electric-blue bands — no dullness, no haziness, no broken pattern. The eyes should be clear, the gill movement rhythmic, and the fish should feed in front of you on demand.

The most important thing to look for is *pinching*. Pinching is the marine-fish term for a hollow, sunken belly that indicates starvation and is the single biggest red flag in any large-angel purchase. Look at the fish from above and from the side. The body should be plump and rounded, not concave behind the gill plates. Avoid any fish with visible white stringy feces (internal parasites), black scarring on the body (handling damage), or cloudy eyes (bacterial issues).

Always ask the store to feed the fish in front of you. A koran that refuses food at the LFS will refuse food at home. Walk away from the sale rather than gamble on a fish that "just hasn't settled in yet."

### Buyer Checklist

- [ ] Body is plump and rounded, no pinched abdomen behind the gills
- [ ] Juvenile pattern is sharp with bright white and electric-blue bands
- [ ] Fish swims confidently in open water and reacts to your presence
- [ ] All fins fully extended; no clamping, splitting, or red streaking
- [ ] Eyes are clear and bright; gill movement is rhythmic and unlabored
- [ ] Feeds eagerly when offered food in front of you at the store
- [ ] No white stringy feces, black handling marks, or visible parasites
- [ ] Store can confirm the fish has been in their system for at least 7-10 days

### Acclimation Protocols for Large Saltwater Fish

Slow drip acclimation is the standard for large angels. Float the bag for 20 minutes to equalize temperature, then transfer the fish and bag water into a clean bucket and run airline tubing as a slow drip from the quarantine tank — about 2 to 4 drips per second — for 60 to 90 minutes until the bucket water has tripled in volume. Discard the original shipping water; do not pour it into your tank.

Test the koran's reaction throughout. A relaxed fish will swim normally; a fish flaring gills, twitching, or flipping is showing acclimation stress and may need the drip slowed further. Move the fish to quarantine — never the display tank, regardless of where it came from — and run the full 30-day QT before introduction. For a deeper walkthrough see our [how to acclimate fish guide](/guides/how-to-acclimate-fish).

If you are still designing the system that will house your koran, our [saltwater aquarium guide](/guides/saltwater-aquarium) covers tank size, equipment, and stocking sequence end to end.

**Find a local fish store** — [Find stores near me](https://www.fishstores.org/near-me)

## Quick-Reference Cheat Sheet

A summary you can screenshot for the fish room:

| Stat            | Value             |
| --------------- | ----------------- |
| Scientific name | P. semicirculatus |
| Adult size      | 12-15 in          |
| Lifespan        | 15-20 yrs         |
| Min tank        | 250 gal           |
| Temperature     | 72-78 degF        |
| Salinity        | 1.020-1.025       |
| pH              | 8.1-8.4           |
| Diet            | Spongivore        |
| Reef safe       | With caution      |

The koran angelfish is not a casual purchase, and the fish you bring home will not look like the fish you keep three years later. Plan for the adult — 15 inches, 250-plus gallons, two decades of feeding sponge formula and watching nitrates — and you will be rewarded with one of the most charismatic centerpiece fish in the marine hobby. Skip the planning, and you will become another data point in the sad statistics of large angels rehomed before their first birthday. Build the right tank first, then go shopping.

## Frequently Asked Questions

### Are Koran Angelfish reef safe?

They are considered reef safe with caution. While they rarely bother SPS corals, they are notorious for nipping at LPS, zoanthids, and clam mantles. In a large, well-fed tank, damage may be minimized, but they are generally not recommended for pristine reef displays.

### How big do Koran Angelfish get?

In a home aquarium, they typically reach 12 to 15 inches. Because of their massive adult size and active swimming nature, they require a minimum of 250 gallons to prevent stunted growth and stress-induced aggression.

### What do Koran Angelfish eat?

They are omnivores with a heavy reliance on sponges and tunicates in the wild. In captivity, feed a variety of high-quality pellets, frozen mysis, and specialized angelfish blends containing sponge matter to prevent nutritional deficiencies.

### Can you keep two Koran Angelfish together?

No, it is highly discouraged. Like most Pomacanthus species, they are extremely territorial toward their own kind and similar-looking species. Unless you have a multi-thousand-gallon system, stick to one per tank.

### Why is my Koran Angelfish losing color?

Fading color is often a sign of poor water quality or Vitamin A/C deficiency. Ensure you are using a high-quality protein skimmer and supplementing their diet with vitamin-soaked seaweed to maintain their vibrant adult hues.

---
*Source: [FishStores.org](https://www.fishstores.org/species/koran-angelfish)*
*Last updated: April 26, 2026*