Common Acan Coral Problems: Tissue Loss, Fading, Pests and Recovery

If your Acan is receding at the edges, washing out to pale, or covered in tiny worms, you need to know which problem you're facing before you can fix it. This guide walks through the three most common symptoms — tissue loss, fading, and pests — and gives a week-by-week plan for stopping the damage and getting the colony to regrow.

What Exactly Is an "Acan"?

"Acan" is trade shorthand for a group of large-polyped stony (LPS) corals that includes Acanthastrea, Micromussa, Homophyllia, and Australomussa. Taxonomists have reshuffled these genera repeatedly — many corals still sold as "Acan lord" are technically Micromussa lordhowensis — but the name on the tag doesn't change how you keep one alive. Husbandry is essentially identical across the whole group, so this article treats them as one coral type.

Quick Visual Triage

Before diving into causes, figure out which category your problem falls into. Look closely under normal lighting and again with a flashlight at an angle.

What you see	Likely category	Jump to
Flesh receding from the skeleton, edges pulling back	Tissue loss	Tissue Loss & Recession
Gel-like, stringy brown film spreading over tissue	Brown jelly infection	Brown Jelly: The Emergency
Coral looks washed-out, pale, or bright white but polyps still extend	Fading/bleaching	Fading and Color Loss
Pinpoint bite marks, worms visible in the mouth folds, poor extension	Pests	Pests on Acan Corals
Polyps stay retracted, deflated, or the mouth gapes constantly	Chronic stress	Healthy vs. Stressed

Core Water Parameters Acans Actually Want

Acans are more forgiving than SPS corals, and chasing "reef-tank-clean" water can actually hurt them.

• Temperature: 76–80°F (24–27°C)
• Salinity: 1.024–1.026 SG
• pH: 7.8–8.4
• Alkalinity: 7–10 dKH, kept stable — swings matter more than the exact number
• Calcium: 380–450 ppm
• Magnesium: 1250–1350 ppm
• Nitrate: roughly 2–10 ppm
• Phosphate: roughly 0.03–0.1 ppm

That nutrient range is worth pausing on: some reefers push toward near-zero nitrate and phosphate the way they would for SPS, but most LPS-focused keepers find Acans hold color and extend better with moderate nutrients. Don't chase zero for this coral — a little "dirtiness" is a feature, not a bug.

Lighting and Flow: The Two Biggest Levers

Lighting: Acans want low-to-moderate light, roughly 50–150 PAR. Place them low or mid-tank, or tuck them into the shade of rockwork. A sudden jump in light intensity is one of the top causes of paling and bleaching, so any change should be gradual.

Flow: Give them low, indirect, turbulent flow so the tissue can inflate fully. Direct blasting flow aimed at an Acan — the kind meant for SPS branching corals — causes chronic non-extension and slow tissue recession over weeks, and it's easy to mistake for disease when it's really just flow damage.

Placement and Aggression

Acans carry long sweeper and feeder tentacles that extend mainly at night, and their sting is strong enough to damage neighboring corals — and to be damaged in return by faster-growing or more aggressive corals nearby.

• Leave at least 2 inches (5 cm) of clearance on all sides.
• If recession or paling shows up only on the side facing a specific neighbor, that's a placement problem, not a disease — move one of the two corals.
• On crowded frag racks, Acans packed too close together sting each other constantly — chemical and tentacle warfare that gets mistaken for infection when the real fix is just more spacing.
• Check for nighttime tentacle extension with a flashlight before assuming a coral is sick. Long, waving tentacles reaching toward a neighbor at night is normal feeding behavior, not distress; persistent daytime retraction and deflation is the real stress signal.

Healthy vs. Stressed Acan

Sign	Healthy	Stressed
Polyp extension (day)	Full, puffy, tissue drapes over the skeleton	Retracted, deflated, skeleton visible through thin tissue
Response to feeding	Mouths open, tentacles reach for food within minutes	No response, or mouth stays gaping afterward
Color	Even, consistent with when purchased	Patchy, pale, or darkening unevenly
Nighttime tentacles	Long sweepers extend, retract by morning	Tentacles out constantly, even at midday

A coral with a mouth that stays open all the time — not just briefly after feeding — is often starving or struggling with water quality, not just "shy."

Tissue Loss and Recession

Tissue receding from the skeleton has several possible causes that overlap enough to require close inspection before treating:

• Brown jelly infection — rapid, gel-like sloughing tissue starting at an old sting or injury site, able to spread across a colony in 24–48 hours (covered in detail below).
• Bacterial infection (STN/RTN-like) — slower or faster tissue peeling without the obvious jelly film.
• Pest damage — flatworms or other pests causing localized tissue death.
• Poor flow or placement — chronic, slow recession concentrated on one side.
• Parameter swings — recession appearing tank-wide after a dosing mistake or missed water change.
• Old frag plug tissue — cosmetic recession off a dying plug edge left over from propagation, not an active infection.

Don't overlook tank age either: as a tank matures, coralline algae and film algae competing for space at the coral's base can slowly encroach onto the skin, mimicking tissue loss. Keep the skeleton margin around the coral's base clean and free of detritus so you can tell the difference.

Brown Jelly: The Emergency

Brown jelly disease is the one Acan problem that calls for immediate action, not a wait-and-see approach. Whether it spreads mainly through direct contact or can travel through the water column is debated, but the practical answer is the same either way: treat every case as fast-spreading and isolate the coral immediately.

Treatment steps:

1. Isolate the affected coral in a separate quarantine or dip container — don't treat it in the display.
2. Physically remove the jelly using a turkey baster or syringe underwater, working carefully so removed material doesn't touch other tissue or spill back into the container.
3. Dip the coral after removal. An iodine-based dip (such as Lugol's solution) is the standard first-line treatment; a hydrogen-peroxide dip or a commercial coral dip are reasonable alternatives.
4. Frag away spreading tissue. If the jelly keeps advancing despite removal and dipping, cut into clean, healthy tissue with a fresh razor or bone cutter, discarding the dead or actively infected piece.
5. Return to the tank only once the jelly is gone, in a low-flow, low-light spot to reduce further stress.

Waiting even a day to act is the most common mistake — brown jelly can consume an entire colony within 24–48 hours if left untreated.

Fading and Color Loss

A pale or washed-out Acan is usually a light problem, not a nutrient problem — though both can be involved.

• Too much light, or a light change that happened too fast. The coral responds by shedding pigment and reducing its zooxanthellae density to protect itself, which shows up as fading toward white or pastel tones.
• Chronically low nutrients. Near-zero nitrate and phosphate can starve the zooxanthellae the coral depends on for color and energy.
• General stress from unstable water chemistry can also present as fading, independent of light or nutrients.

Fix: Reduce PAR or relocate the coral higher/deeper as needed, and make any lighting change gradual — acclimate over 2–4 weeks, not days. Let nutrients run at the moderate end of the range rather than scrubbing them out, and resume regular target feeding.

Pests on Acan Corals

• Acan/LPS flatworms — small flatworms specific to this coral group, causing pinpoint tissue damage and preventing full polyp extension. Treat with a coral dip and manual removal by blasting the colony with a turkey baster; repeat over several days since eggs can survive a single treatment.
• Nudibranchs — less common on Acans than on some other LPS but still possible. Manual removal plus dipping is the standard approach.
• Snails or hermit crabs bothering the tissue — reposition or remove the offending tank inhabitant rather than treating the coral.
• Aiptasia or other pest anemones growing nearby can sting an Acan even without direct contact; treat the pest anemone separately rather than assuming the Acan itself is diseased.

You can browse dip solutions and treatment products, along with quarantine-friendly coral options, in FishyHub's LPS hard corals category and treatment and medication section.

Fragging a Declining Colony

When recession keeps spreading despite treatment, cutting away the dead tissue promptly is better than waiting to see if it stops on its own — and fragging lets you rescue part of a colony that's otherwise doomed.

1. Use a clean, fresh razor blade or coral bone cutters; dull or reused tools introduce more bacteria.
2. Cut well into visibly healthy tissue, leaving a margin beyond where recession appears to have stopped — damage often extends further than it looks.
3. Dip the freshly cut piece the same way you would treat a brown jelly case, since a fresh cut is an open wound.
4. Place the rescued piece in low flow and low light for the first one to two weeks, exactly as you would a new frag.

Keep the skeleton of the original colony clean of algae and detritus — a stable base with even a small living patch can often recover fully once the underlying cause is fixed.

A completely bare skeleton with zero remaining tissue will not regrow coral, though coralline algae may eventually colonize it.

Acclimating New Frags

New arrivals need a gentler introduction than an established colony. Drip acclimate to match temperature and salinity slowly rather than a quick dunk, then place the frag in a dark, low-flow "quiet corner" for the first 1–2 weeks instead of under full display lighting. Delay target feeding until polyps are extending normally, and dip and quarantine every new Acan before it goes near the display — this single step is the most effective way to keep flatworms and brown jelly out of an established tank.

Target feeding with meaty foods, pellets, or a gel-type blend 1–3 times per week doubles as both a health indicator and a recovery tool — a coral that reliably reaches for food is telling you the husbandry is working.

Common Mistakes to Avoid

• Placing a new frag directly under high-intensity SPS-level lighting, causing immediate bleaching.
• Running strong, direct flow meant for SPS corals, leading to chronic non-extension and slow recession.
• Waiting too long to act on brown jelly, letting it spread across the whole colony within a day or two.
• Overcrowding a frag rack so Acans sting each other, then misdiagnosing the damage as disease.
• Skipping quarantine and dipping on new arrivals, introducing flatworms or jelly infection to an entire tank.
• Assuming a bare skeleton patch is automatically dead, when tissue can sometimes regrow once the cause is corrected and the area is kept clean.

Frequently Asked Questions

Why is my Acan losing tissue from the edges inward?

This is usually flow or placement stress, a sting from a neighboring coral, or an early bacterial or brown jelly infection. Isolate the coral and inspect closely for a gel-like film before deciding on treatment.

Can a fully bleached (white) Acan skeleton recover?

Only if some living tissue remains somewhere on the colony. A totally bare skeleton with no tissue at all is dead and will not regrow coral, though coralline algae may eventually colonize the surface.

Is brown jelly disease contagious to other corals?

It can spread quickly, whether by direct contact or debris in the water column, so treat every case as an emergency. Isolate the affected coral immediately rather than attempting treatment in the display tank.

How often should I feed my Acan coral?

Roughly 1–3 times a week with meaty or pellet-type foods works for most tanks. Feed more often if nutrient levels run low or the coral's color starts to look pale.

What flow and light does an Acan coral need?

Low, indirect flow and low-to-moderate light, roughly 50–150 PAR, placed low in the tank or in partial shade of rockwork. Sudden increases in either are the most common cause of stress in this coral.

Why did my Acan fade to pale or white after I upgraded my lights?

A sudden increase in light intensity causes the coral to shed pigment and reduce its zooxanthellae, which shows up as fading. Ease into any new lighting setup over 2–4 weeks, and consider raising the frag or dimming the fixture during the transition.

How do I get rid of flatworms on my Acan?

Dip the coral outside the display using an iodine-based or coral-safe flatworm treatment, then physically blast and remove visible worms with a turkey baster. Repeat every few days since flatworm eggs commonly survive a single treatment.

How long does it take an Acan to recover after fragging away dead tissue?

Visible healing or skinning-over can begin within days to a couple of weeks. Full tissue regrowth over the cut skeleton typically takes several weeks to a few months, depending on colony size and stability of conditions.

Once you've identified the cause and corrected flow, light, or water chemistry, browse FishyHub's corals category for healthy, quarantine-ready Acan frags and other LPS to build out your recovering reef.