Saltwater Fish · Tangs

Regal Blue Tang

Paracanthurus hepatus

Large, active reef fish needing serious swimming spaceAdvanced

Lifespan: 10-20+ years
Size: 10-12 in
Social needs: Best kept one per tank unless the system is very large
Time: High
Cost: High
Diet: Omnivore (meaty marine foods plus marine algae)

Overview

What is this animal?

The Regal Blue Tang is a large, active reef fish that grows far bigger and lives far longer than most buyers expect.
Reaching up to 12 in, it is a fast, near-constant swimmer that quickly outgrows the small tanks it is often sold for.

This is an advanced fish.

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It needs a large, mature reef system, stable water, and an experienced keeper prepared for a decades-long, expensive commitment.
It is frequently sold to beginners who lack the space and equipment it requires.

Temperament

Generally peaceful toward other species but territorial toward other tangs and its own kind, especially in cramped quarters.
A single specimen per tank is safest unless the system is very large and well aquascaped.

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Newly added fish are often shy and may hide or wedge into rocks.
With time and space they become bold, active centrepiece fish that need room to roam.

A good fit for

Experienced reef keepers with large systems
Hobbyists wanting a long-term centrepiece fish
Keepers committed to quarantine protocols
Those with the budget for a large setup

Common mistakes to avoid

Sold small, but grows to 12 in and outgrows small tanks
Prone to marine ich and velvet
Buying without a large, mature reef ready
A poor or unvaried diet, which is linked to HLLE

Enclosure

Minimum 1,320 gallons

One of its kind per tank; other compatible species can share it. Best kept one per tank unless the system is very large

Provide an established reef aquarium of at least 1,321 gallons and at least 8 ft long for an adult, with open swimming space along its length and live rock with caves it can dart into when stressed.
Practical Fishkeeping gives a juvenile a tank at least 5 ft long and a large adult one close to 8 ft, holding potentially over 265 gallons, and a German reef encyclopedia asks more than 530 gallons for an adult.
This guide asks for more because good conditions are never less than a law requires, and Austria's law asks 1,320 gallons for a tang that grows past 10 in.

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Care listings that give 180 gallons and a 6 ft tank are far too small for a fish that reaches 12 in.
It is reef-safe and benefits from strong flow and good oxygenation.

Keep parameters stable: temperature 75-81°F, salinity 1.024-1.026, pH 8.1-8.4, ammonia and nitrite at zero, and nitrate low.
A fully cycled, biologically mature tank is essential before introduction.

Check your enclosure

Supplies

Setup

Tank, stand and sump
Return pump and powerheads
Protein skimmer
Reef lighting
Rock and sand

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Salt mix, refractometer and test kits
Quarantine tank

Ongoing

Dried marine algae (nori) sheets in bulk
Magnetic or suction veg clip
Algae or herbivore pellets
Herbivore frozen food blend
Frozen mysis and other meaty marine foods (a small share for the yellow tang, a daily staple for the regal blue tang)

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Vitamin or HUFA soaking supplement
Second clip so nori can be offered in two places

Safe substrate: Aragonite sand · Dry or cured live rock

Work out the cost

Care routine

Daily

Check salinity, temperature and flow
Clip on dried algae
Feed
Head-count and look everyone over
Top up evaporation with fresh water

Every few days

Service the skimmer and filter socksevery 3 days

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Weekly

Check head, lateral line and flanks
Clean the glass
Test the water
Water change

Monthly

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

Health review: Quarterly review with an HLLE check, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Omnivore (meaty marine foods plus marine algae)

Unlike the yellow tang, the Regal Blue Tang feeds mainly on zooplankton in the wild and grazes algae as well, so it needs both.
Feed several times a day: frozen mysis, enriched brine and other meaty marine foods plus a quality marine pellet, and clip dried nori or seaweed sheets in the tank daily so it can graze.

Frequent grazing supports digestion and reduces aggression.
A varied diet with added vitamins helps prevent head and lateral line erosion (HLLE), which is linked to poor nutrition and water quality in tangs.

Health

Signs of good health, and the common problems

Blue tangs are prone to marine ich (Cryptocaryon) and velvet, partly because of their thin scaling and sensitivity to stress.
Quarantine every new fish and minimise stress during transport and acclimation.
They tolerate copper-based treatment well, which is a useful tool in a hospital tank.

Watch for white spots, scratching, rapid breathing, and faded colour.
Head and lateral line erosion points to poor diet or water quality.
Stable conditions and good nutrition are the best preventatives.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

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

Any detectable ammonia or nitriteWater change now with matched, mixed and aerated saltwater. Stop feeding. Ammonia is directly toxic, and at reef pH more of it is in the toxic form, so a marine system has less margin than a freshwater one. Nitrite is far less toxic in seawater, but any reading in a stocked tank means the biological filter is not keeping up.

Now

Temperature or salinity has moved sharplyCorrect slowly, over hours, not minutes. Check the heater and the top-off. The speed of the change does the damage. Correcting fast repeats the injury in the other direction.

Now

Rapid gilling, or a fish hanging in the flow breathing hardIncrease aeration and check temperature and salinity. Warm water holds less oxygen, and a heater failure shows up here first.

Now

Today

White spots, or a fine dusting like icing sugarIdentify which parasite before treating. Most reef tanks cannot be treated in place. The two common parasites look similar and need different handling; velvet can kill a tank in days.

Today

Corals closed for more than a day, or receding tissueTest alkalinity first, and compare it against the last reading rather than a target. Unstable alkalinity is the most commonly cited coral killer, and a swing shows up in the trend, never in a single point.

Today

A new fish added without quarantine now looks unwellRemove it to a separate system today if you can. Nearly every wipeout in a reef tank traces back to a skipped quarantine.

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.

Bedding and substrate

2 safe, 3 with a caveat, 2 to avoid

In a marine system the rock and the sand are life support, and how you start them decides the first six months.

Safe

Aragonite sandThe standard marine substrate, and it hosts the biology. It does not meaningfully hold pH or alkalinity at normal reef pH, so test and dose for those regardless.

safe

Dry or cured live rockDry rock avoids importing pests but takes longer to mature. Cured rock is faster and riskier.

safe

With a caveat

Deep sand bedsPowerful nutrient processing when they work and a sulphide release when they are disturbed. Choose shallow or deep deliberately, not by accident. A sand-sifting or burrowing goby needs a fine bed about 2 to 3 in deep that it turns over itself. That is a different thing from a denitrifying deep sand bed (4 in or more, left undisturbed), and the two do not mix: a sifting goby disturbs the layers a deep sand bed depends on and eats the life in it.

with a caveat

Uncured live rockIt will cycle the tank for you, and it will also bring in whatever was living in it.

with a caveat

Bare bottomWorkable in high-flow systems for fish that neither sift nor burrow, but it removes a large part of the biological buffer. Wrong for watchman gobies and other gobies that burrow or sift, which need a fine sand bed at least 2 in deep to dig and feed in, and for mandarins and other copepod-eaters, which need sand as well as mature rock for their food to breed in.

with a caveat

Never

Silica play sandNot the marine standard, and commonly blamed for feeding diatom blooms in a new tank.

never

Any rock or decor of unknown originMetals and phosphate leach for months and are almost impossible to trace once the tank is running.

never

This is our general list for saltwater fish. We have not built one specific to Tangs yet.

Top resources for more info

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