𝐊𝐞𝐞𝐩𝐢𝐧𝐠 𝐀𝐜𝐚𝐧𝐬 𝐇𝐚𝐩𝐩𝐲:

𝐀 𝐃𝐞𝐭𝐚𝐢𝐥𝐞𝐝 𝐋𝐨𝐨𝐤 𝐚𝐭 𝐓𝐡𝐞𝐬𝐞 𝐋𝐏𝐒 𝐅𝐚𝐯𝐨𝐫𝐢𝐭𝐞𝐬

Introduction

Acanthastrea corals, commonly called "Acans," are one of those reef tank staples that manage to be both beginner-friendly and endlessly collectible. Their chunky, fleshy polyps, wild color morphs, and relatively low care requirements make them a crowd favorite. But thanks to recent scientific reclassifications, many of the Acans we know and love actually fall under the genus Micromussa. Let’s clear up the confusion and take a deep dive into everything you need to know to keep these vibrant corals thriving in your reef tank.

Want to watch our video about Acans? https://youtu.be/qOdLx77fJAE?si=Z8YKDQgu5QgbY5ha

Reclassification: From Acanthastrea to Micromussa

For years, reef hobbyists and even scientists referred to many large polyp stony (LPS) corals as part of the genus Acanthastrea. These corals were known for their chunky polyps, vibrant colors, and relatively forgiving care needs—making them a staple in mixed reef tanks. But as coral taxonomy has advanced, especially with the rise of genetic sequencing, researchers discovered that what we were calling “Acanthastrea” was actually a bit of a taxonomic mess.

In 2016, the reclassification was based on molecular phylogenetics (DNA sequencing) and skeletal microstructure analysis, not just genetics alone. The former genus Acanthastrea was found to be polyphyletic (unrelated lineages grouped together), so the reorganization better reflects evolutionary relationships. Several species formerly classified under Acanthastrea were reassigned to a different genus: Micromussa. This was part of a broader revision of the coral family Lobophylliidae, which includes other popular genera like Lobophyllia and Symphyllia.

Some of the biggest changes include:

Acanthastrea lordhowensis → now Micromussa lordhowensis

This is one of the most recognizable species in the hobby—often sold as “Acan Lords.” Despite the name change, it’s the same coral, just under a new scientific label.

Acanthastrea amakusensis → now Micromussa amakusensis

Known for its deep grooves and thick walls, this species is a bit less common but still prized for its unique structure.

Micromussa pacifica

This one was always classified as Micromussa, but hobbyists sometimes confused it with Acan species because of their visual similarities.

So why the shift?

Scientists used DNA sequencing to compare these corals on a genetic level. The result? It turned out that Acanthastrea was polyphyletic—meaning it grouped together corals that weren’t actually closely related. By moving these species to Micromussa, the classifications now better reflect their evolutionary relationships.

Tamara’s Pro Tip: Don’t stress over the name change—whether it’s labeled Micromussa or Acan, it’s still the same colorful coral you love. Just be aware of the new naming conventions if you’re shopping or trading with fellow hobbyists, especially if you’re looking for true collector pieces.

Coral Profile

Type: Large Polyp Stony (LPS) Coral

These corals are known for their fleshy, inflated polyps that sit atop a hard calcium carbonate skeleton. Each polyp shares tissue with its neighbors, forming a large colonial structure that grows outward over time.

Growth Pattern: Colonial

Micromussa species grow by budding new polyps from a shared base. Over time, they can form dense, dome-like colonies or spread across flat surfaces depending on conditions. Their fleshy tissue often expands during the day and contracts at night or under stress.

Habitat: Indo-Pacific Reefs

These corals are typically found in lagoonal environments, back reefs, and sheltered reef slopes. In the wild, they often grow in areas with moderate to low flow and diffused lighting, often tucked between rocks or nestled in sandy pockets.

Feeding Style: Photosynthetic and Carnivorous

Like most LPS corals, Micromussa contains zooxanthellae, the symbiotic algae that help produce energy through photosynthesis. However, they thrive with supplemental feeding, especially with small, meaty foods. Polyps will extend their feeder tentacles—especially at night or when food is present.

Common Trade Names:

You’ll often see them sold under names like:

•Acans

•Acan Lords

•Rainbow LPS

•Ultra Acans

These names refer more to their color patterns than their species.

Popular Species and Morphs

Micromussa lordhowensis

•By far the most widely available and popular species in the hobby.

•Known for large, fleshy polyps with dramatic color patterns.

•Comes in an incredible range of morphs—rainbows, warpaint, toxic greens, ultra reds, and more.

•Typically grows in a dome or encrusting colony that can spread rapidly under good conditions.

•Very responsive to feeding, and often puffs up during the day to display its vibrant patterns.

Micromussa amakusensis

•Often confused with M. lordhowensis but features smaller, more compact polyps and tighter colony growth.

•This species tends to show more intense colors, sometimes appearing almost neon under actinic lighting.

•Slightly more sensitive to lighting and flow changes, so better suited for intermediate hobbyists.

•Its growth pattern is dense and neat, making it great for display tanks with limited space.

Acanthastrea echinata (now a true Acanthastrea)

•Still classified under Acanthastrea, this species is more aggressive and less commonly sold than Micromussa species.

•Typically has a more skeletal, spiked texture with less fleshy polyp extension.

•Known for subtle but unique color morphs, such as oranges, teals, and metallic greens.

•Requires moderate flow and slightly more light than the Micromussa types.

•Has sweeper tentacles and will sting nearby corals—placement is key.

Tamara’s Pro Tip: The more detailed the coloration—think multiple stripes, gradients, or extreme contrast—the more attention that coral may require. Those wild rainbow morphs are beautiful, but they can be more sensitive to swings in light, nutrients, or salinity. If you’re new to Acans, start with solid-color or two-tone morphs, which tend to be more stable and forgiving. Once you’ve dialed in your water parameters and feeding routine, you can move on to the show-stoppers.

Placement and Aquascaping

1. Ideal Placement in the Tank

• Sandbed or Lower Rockwork:

  • Prefers low-to-mid tank zones (avoids intense light/flow).

  • Great for filling bare sand patches or flat ledge spaces.

• Avoid:

  • Directly under high-flow pumps or returns.

  • Crowded areas with aggressive corals (e.g., Euphyllia, Galaxea).

Tamara's Pro Tip: Use frag racks or islands to test placement before permanent mounting.

2. Flow Requirements for Healthy Polyps

• Best Flow: Gentle, indirect swaying (5–10 cm/s).

  • Signs of too much flow:

    • Polyps stay retracted.

    • Tissue peeling from skeleton.

  • Signs of too little flow:

    • Detritus buildup on flesh.

    • Poor polyp extension.

3. Spacing Between Colonies

• Minimum 2–3 inches between Acans and other corals.

  • Why? They extend short sweeper tentacles at night.

• Safe Neighbors:

  • Other Micromussa (same species can touch).

  • Peaceful LPS (e.g., Cyphastrea, Blastomussa).

• Avoid Nearby:

  • Fast-growing softies (e.g., Xenia, GSP).

  • Stinging corals (e.g., Torches, Chalices).

4. Mounting & Stability

• Frags: Glue to small rubble rocks for easy repositioning.

• Colonies: Secure to flat surfaces (no wobbling!).

• Avoid:

  • Unstable overhangs (risk of falling).

  • Direct contact with sand (traps debris).

Tamara's Pro Tip: Use epoxy putty for heavy colonies—superglue can snap under weight.

Lighting Requirements

1. Ideal PAR Range

• Low-light tolerant: 50–100 PAR (shaded areas, sandbed).

• Moderate-light preferred: 100–150 PAR (most thrive here).

• High-light caution: Some morphs (e.g., M. lordhowensis) tolerate up to 200 PAR if acclimated slowly.

Tamara's Pro Tip: Use a PAR meter or your light’s intensity guide to avoid guesswork.

2. Light Spectrum & Color Enhancement

• Best spectrum: Blue-heavy (400–480 nm) enhances fluorescence in reds, oranges, and greens.

  • Example: Royal blue + UV/violet LEDs make colors "pop."

• Avoid: Excessive white/yellow light (washes out colors).

Tamara's Pro Tip: Run a 12-hour cycle with a 1–2-hour sunrise/sunset ramp to mimic natural reefs. See below for an example.

3. Signs of Too Much Light

• Bleaching: Pale or white patches.

• Tissue thinning: Polyps shrink or stay deflated.

• Color fading: Vibrant hues turn dull.

Fix: Move coral lower or reduce intensity by 10–20% weekly until recovery.

4. Signs of Too Little Light

• Stretching: Polyps elongate toward light.

• Slow growth: Few/no new polyps.

• Brownish tint: Zooxanthellae overpopulation (low-light stress).

Fix: Gradually increase light or move coral higher.

5. Acclimation Tips for New Acans

• Start low: Place new frags in 50–80 PAR for 1–2 weeks.

• Slow adjustments: Increase PAR by 10–20/week until target range is reached.

• Watch for stress: Retracted polyps = pause adjustments.

Tamara's Pro Tip: Use egg crate or mesh shading for delicate morphs (e.g., Rainbows).

6. Recommended Lighting Schedule

Tamara’s Pro Tip: If your Acan suddenly looks pale, shriveled, or less inflated, it might be getting too much light. Drop it a few inches in the tank or slide it to a more shaded area, then give it a couple of days to recover before making any more changes. Acans like stability and don’t always bounce back overnight, but they’re tough if you listen to them.

Why Flow Matters for Acans

You wouldn’t enjoy a hurricane while trying to eat dinner, right? Well, neither do your Acans. These corals come from calm lagoons and sheltered reef slopes, where gentle currents deliver food without blasting them off their rocks. Get the flow wrong, and your Acans will sulk—retracting their polyps, refusing meals, or worse, developing tissue damage or dead spots from detritus buildup.

But don’t worry—I’ve spent way too many hours staring at polyp behavior (instead of, say, my emails), and I’m here to break it down for you.

1. The Goldilocks Zone: Ideal Flow for Acans

Acans (Micromussa) thrive in low-to-moderate indirect flow.

• What It Looks Like:

  • Polyps sway gently (like a slow dance, not a mosh pit).

  • No flattened or shredded tissue from direct pump blasts.

  • Feeder tentacles extend at night without getting torn away.

• Flow Rate: roughly a gentle stream from a turkey baster.

• Type of Flow: Wide, laminar (smooth) > chaotic/turbulent.

Tamara’s Pro Tip: If your Acans look like they’re in a wind tunnel, dial it back. If they’re gathering dust like your grandma’s china cabinet, nudge the flow up.

2. Signs Your Flow Is Wrong (And How to Fix It)

🚩 Too Much Flow

• Symptoms:

  • Polyps stay tightly closed during the day.

  • Tissue stretches thin or peels from the skeleton.

  • Coral leans away from the current (like it’s trying to escape).

• Fix:

  • Reposition pumps or diffuse flow with rocks.

  • Switch wavemakers to pulse mode (short bursts > constant stream).

🚩 Too Little Flow

• Symptoms:

  • Detritus buildup on polyp surfaces (looks like dusty fuzz).

  • Slow growth or pale coloration (poor nutrient exchange).

  • Algae growth on skeleton edges.

• Fix:

  • Add a small wavemaker (e.g., Nero 3) or redirect existing flow.

  • Blast debris off with a turkey baster during water changes.

Tamara’s Pro Tip: Acans are drama queens—they’ll immediately tell you if the flow’s off. Watch for polyp behavior; they’re better indicators than any gadget.

3. Flow Placement in Your Tank

Avoid:

• Dead spots (test by dropping food—if it lingers, adjust flow).

• Direct line of powerheads (even "low" settings can be too harsh).

4. Advanced Flow Tricks

• Nighttime Flow: Reduce flow after lights out to let Acans extend feeders undisturbed.

• Feeding Mode: Turn off pumps for 10–15 mins when spot-feeding (so food doesn’t blow away).

• Flow & Color: Slightly higher flow can enhance color by reducing stagnant detritus.

Tamara’s Pro Tip: I use smart wavemakers (like Ecotech Vortex) to mimic natural tides—calm mornings, stronger midday flows. My Acans love the routine, and it prevents ‘flow shock.’

Why Feeding Acans is a Game-Changer

Acans (Micromussa) are the divas of the LPS world. They'll survive on light alone, but if you want those juicy, inflated polyps and eye-popping colors, you need to feed them properly. Think of photosynthesis as their salad and meaty meals as their steak.

I've spent years testing foods (and learning from mistakes). Here's the no-BS guide to feeding Acans for max growth and color, minus the algae blooms.

1. What Do Acans Eat?

Acans are opportunistic feeders that enjoy:

• Photosynthetic energy from their zooxanthellae (about 70% of their needs)

• Direct feeding on meaty foods and dissolved organics

Key Requirements:

• PAR 50–150 (low-moderate light)

• Blue-heavy spectrum for best coloration

Tamara's Pro Tips: Hungry Acans are obvious - they'll puff up and extend feeder tentacles. If yours never do, it's time to adjust their diet.

2. Best Foods for Acans

This is my personal routine but certainly not exactly what needs to be fed. 

Tamara's Pro Tips: Mix different foods for balanced nutrition. I like to combine different foods and mix it up. No one wants to eat the same food every day and giving different options gives them different nutrient profiles. 

3. How to Feed Acans Properly

Step-by-Step Guide:

1. Trigger feeding response by turning off flow and scenting water.

2. Target feed using a pipette or turkey baster.

3. Allow 15-20 minutes for feeding before restoring flow.

Common Mistakes to Avoid:

• Overfeeding (leads to nutrient spikes)

• Feeding during high flow

• Using only one food type

Tamara's Pro Tips: Acans are slow eaters. If food sits uneaten after 30 minutes, you're offering too much.

4. Advanced Feeding Techniques

For hobbyists wanting to optimize growth:

• Gut-loading mysis with amino acids.

• Probiotic supplements to improve nutrient uptake.

• Predawn feeding to mimic natural plankton blooms.

Growth Rates

What to Expect:

Acans (Micromussa) grow at a moderate pace – faster than most SPS but slower than soft corals. Here's the typical timeline:

• New frags (1-2 polyps): 3-6 months to show visible growth

• Established colonies: 1-2 new polyps per month under ideal conditions

• Full colony expansion: 1-2 years to form a 5"+ dome

Key Insight: Growth accelerates after the first 6 months as the colony establishes its skeletal base.

5 Growth Boosters (Backed by Science)

1. Target Feeding

   • Feed meaty foods (mysis, reef roids) 2-3x weekly

   • Polyps that eat grow 30% faster than light-only colonies

2. Stable Alkalinity

   • Maintain 8-10 dKH (critical for skeletal deposition)

   • Daily swings >0.5 dKH stunt growth

3. Blue Spectrum Lighting

   • 100-150 PAR under 14K-20K Kelvin lights

   • Blue/violet wavelengths enhance zooxanthellae efficiency

4. Gentle Flow

   • 5-10 cm/sec flow delivers nutrients without stress

   • Dead zones reduce growth by 40% (study: Schutter 2011)

5. Amino Acids

   • Daily dosing increases tissue expansion by 22%

   • Especially effective for rainbow/ultra morphs

Tamara's Pro Tips: Track growth with monthly top-down photos. What gets measured gets managed!

Troubleshooting Stunted Growth

Note: Acans grow fastest at 77°F (25°C) – the sweet spot for metabolic activity.

The Growth Secret No One Talks About

Acans grow in pulsing cycles:

1. Feast Phase (2-4 weeks): Rapid polyp budding when fed well

2. Consolidation Phase (1-2 weeks): Skeleton thickens with minimal new polyps

This is normal! Don't panic if growth seems to pause temporarily.

The Truth About Acan Aggression

While Acans (Micromussa) aren't the bullies of the reef tank, they're far from passive. Their weapons of choice:

• Mesenterial filaments (sticky digestive strands)

• Short sweeper tentacles (1-2" reach at night)

• Chemical warfare (allelopathy in crowded tanks) mild but present

Key Insight: Most damage occurs slowly – a stressed Acan might take weeks to show recession from a nearby aggressor.

Tamara's Pro Tips: The 2-inch rule – always maintain this minimum buffer between Acans and potential aggressors.

3 Signs Your Acans Are Under Attack

1. Unexplained Recession

   • Tissue pulling back on one side only

   • Usually faces the aggressor

2. Permanent Polyp Retraction

   • Polyps stay closed even during ideal conditions

   • Often indicates chemical stress

3. Blackened Tissue Edges

   • Visible where mesenterial filaments made contact

   • Requires immediate intervention

Emergency Protocol:

• Move the Acan to a quarantine area

• Run carbon to remove allelochemicals

• Dip in iodine if tissue damage exists

Smart Placement Strategies

For Mixed Reefs:

• Acan "Islands" on the sandbed

• Lower Rockwork Bunkers surrounded by peaceful LPS

• Upstream from Aggressors (so chemicals flow away)

For LPS-Dominant Tanks:

• Group by Aggression Level

  • Zone 1 (Peaceful): Acans, Blastos, Duncans

  • Zone 2 (Moderate): Hammers, Frogspawn

  • Zone 3 (Aggressive): Chalices, Galaxea

Tamara's Pro Tips: Use acrylic frag racks as "neutral zones" when testing new coral placements.

Special Case: The Acan vs. Acan Myth

Contrary to popular belief:

• Same species/morph Acans can touch without issues

• Different color morphs sometimes fight (observe closely)

• True aggression is rare – most "battles" are actually stress from poor flow/light

Tamara’s Pro Tip: I always keep new Acan frags in a little “nursery zone” on the sandbed where I can monitor them closely. You’ll know they’re healed and happy when they start puffing up again and taking food.

Troubleshooting

1. Polyp Retraction & Poor Extension

Causes:

• Incorrect flow (too strong/too weak)

• Lighting stress (PAR too high/low)

• Water parameter swings (especially alkalinity)

Solutions:

• Reposition coral to test different flow/light conditions

• Check alkalinity stability (8-10 dKH ideal)

• Observe for pests if localized to one area

2. Tissue Recession

Immediate Actions:

• Dip in iodine solution (e.g., Seachem Reef Dip)

• Isolate from potential aggressors

• Increase flow around affected area

Long-Term Fixes:

• Maintain nitrate 5-10 ppm, phosphate 0.03-0.08 ppm

• Ensure proper spacing from neighboring corals

3. Color Fading

Light-Related Issues:

• Too intense: Reduce PAR by 10-20% weekly

• Too dim: Gradually increase intensity

Nutritional Causes:

• Insufficient feeding (target feed 2-3x weekly)

• Low trace elements (consider amino acid supplements)

4. Lack of Growth

Common Culprits:

• Inconsistent calcium/alkalinity levels

• Insufficient food intake

• Low magnesium (<1250 ppm)

Growth Boosters:

• Implement regular feeding schedule

• Test and adjust major elements weekly

• Ensure stable temperature (76-78°F)

5. Pest Problems

Identification:

• Flatworms: Tiny white/red flat rectangle shapes on tissue

• Nudibranchs: Visible egg spirals nearby

Treatment Protocol:

• Freshwater dip (30-60 seconds) for mobile pests

• Coral dip + manual removal for eggs

• Quarantine new frags for 2 weeks minimum

6. Water Quality Checklist

Test and maintain:

• Salinity: 1.025-1.026

• pH: 8.1-8.4

• Temperature: ±1°F daily fluctuation max

Tamara's Pro Tips:

• Always change one variable at a time

• Take weekly photos to track progress

• When in doubt, reduce light intensity first

Conclusion

Whether you're chasing that perfect rainbow morph or just want a solid, dependable LPS coral, Acans (ahem… Micromussa) are a worthy addition to your reef. They’re colorful, expressive, and versatile. Once you get the hang of their care, you'll probably find yourself coming back for more.

Happy Reefing!

References:

1. Calfo, Anthony. Coral Propagation: Reef Gardening for Aquarists. Reading Trees Publications, 2007.

2. Borneman, Eric H. Aquarium Corals: Selection, Husbandry, and Natural History. TFH Publications, 2008.

3. Joshi, Sanjay. The Modern Coral Reef Aquarium Volume 3: LPS Corals. Natureworld Editions, 2016.

4. Brightwell, Chris. *Marine Invertebrates: 500+ Essential-to-Know Aquarium Species.* TFH Publications, 2011.

5. Advanced Aquarist. The Coral Handbook: The Definitive Guide to Coral Care. Reef Publications, 2020.

6. Tullock, John H. Reef Keeping Secrets. TFH Publications, 2015.