Acan Coral Care Guide: Lighting, Flow, Feeding and Placement
Acan corals are one of the most forgiving large-polyp stony (LPS) corals for a home reef tank, but "easy" only holds true if the light, flow, and feeding schedule match what the polyps actually want. This guide gives concrete numbers instead of vague "moderate" advice, so you can set up a new Acan correctly and troubleshoot one that has stopped opening.
What Exactly Is an "Acan" Coral?
"Acan" is the hobby nickname for corals sold under the older genus name Acanthastrea. In 2016, taxonomists reclassified most of these into the genus Micromussa, with Micromussa lordhowensis being the species behind most "Acan Lord" colonies in the trade. The old name stuck in the hobby even though the science moved on, so you'll see both names used interchangeably on care sheets and in the trade.
Acans are rated beginner-to-intermediate friendly. Compared to most LPS, they're hardy, tolerant of parameter swings, and grow relatively quickly once settled, which is why they're a common first LPS purchase for reefers moving up from soft corals.
Lighting: How Much PAR Does an Acan Need?
Acans want low to moderate light, roughly 50–100 PAR as a safe general target. Some colonies do fine as low as 25–50 PAR, and some tolerate up to 150 PAR under stable conditions, but there's no need to chase a single "correct" number — this is a case where a wide safe band and close observation beat a precise target.
Signs you've overshot on light:
- Bleaching or unusually pale, washed-out tissue
- Polyp shrinkage — heads stay puffed tight instead of extending
- Reduced feeding response even when food is offered
Because Acans tolerate lower light well, they're a good candidate for lower or mid-tank placement, tucked under an overhang or on a lower rock ledge rather than sitting directly under an intense fixture. Many reefers also find Acan coloration pops hardest under a blue-heavy, actinic spectrum rather than a bright, white-heavy one. If you're shopping for a fixture that lets you dial intensity down for LPS, browse LED aquarium lighting with adjustable channels.
A Simple Placement Guide by Tank Height
| Position | Approximate PAR | Best for Acans? |
|---|---|---|
| Top of tank, under fixture | 200–400+ | Too intense — bleaching risk |
| Mid-tank, open rockwork | 100–200 | Workable if shaded or fixture is dimmed |
| Mid-to-lower rock ledge, partially shaded | 50–100 | Ideal zone |
| Sandbed or base of rockwork | 25–75 | Fine, especially for new frags |
Use a PAR meter if you have one; if not, treat "lower and shaded" as your default and watch polyp extension over the first two weeks as your feedback signal.
Water Flow: Ambient vs. Direct
This is where most beginners get confused, because "low to moderate flow" gets used two different ways in care advice. It helps to split it into two separate ideas:
- Ambient tank flow (whole-system circulation for gas exchange and keeping detritus in suspension) can reasonably be moderate to high.
- Direct flow hitting the coral itself should be gentle, indirect, and turbulent rather than a laminar jet.
An Acan aimed straight into a powerhead's output stream will show retracted polyps, tissue damage, and discoloration over time, even if your overall tank flow is appropriate for the rest of the reef. The fix is placement, not just turning pumps down: put the colony in a flow "shadow" behind live rock so water swirls around it instead of blasting it directly. You want just enough movement across the polyp surface to prevent detritus from settling and to deliver food particles — not enough to keep the polyps clamped shut.
Water Parameters
Acans tolerate a fairly wide range, and — unlike SPS corals — they handle mildly "dirtier" water reasonably well. That said, stability over time matters more than hitting an exact number.
| Parameter | Target Range |
|---|---|
| Temperature | 72–82°F (22–28°C), tightened to 76–78°F (24–26°C) for stability |
| pH | 8.1–8.4 |
| Specific gravity | 1.023–1.026 |
| Alkalinity | 8–12 dKH |
| Calcium | 350–450 ppm |
| Magnesium | 1250–1350 ppm |
| Nitrate | roughly 1–10 ppm |
| Phosphate | low but nonzero, ~0.01–0.05 ppm |
Tolerating a little nitrate doesn't mean ignoring nutrient export entirely. Skipping water changes for long stretches still lets algae and cyanobacteria creep in, and a film of algae smothering fleshy LPS tissue is a real risk even in a tank that's "technically" within range.
Feeding an Acan Coral
Coral Nutrition Basics
Like most zooxanthellate corals, Acans get the majority of their energy — commonly estimated at roughly 70–90%, depending on the coral and conditions — from photosynthesis via the algae living in their tissue. The rest comes from captured plankton, bacteria, and absorbed dissolved organics. Aquarium water column, however, is far leaner in planktonic food than a wild reef, which is why supplemental feeding measurably helps growth and color even when a colony is surviving fine on light alone.
How Often and What to Feed
Target-feed meaty foods 2–3 times per week. A well-lit, established colony can get by on once a week, and daily feeding is optional rather than necessary — treat any claim that daily feeding is "required" with skepticism.
Good food options include:
- Mysis shrimp
- Chopped table shrimp or other seafood
- Brine shrimp (artemia)
- Copepods
- Prepared frozen or pellet LPS blends
Feed when polyps are extended, which is often in the evening as lights dim, though many Acans adapt to daytime feeding schedules over time.
Target Feeding Technique
Load a syringe or turkey baster with a slurry of food and tank water, then aim it directly at open polyps rather than broadcasting food into the water column. This matters more for Acans than it does for filter-feeding fish, because the coral relies on capturing food that actually reaches its polyps.
Before feeding:
- Turn off or reduce the return pump, skimmer, and any powerheads aimed at the colony.
- Deliver the food slurry directly onto the extended polyps.
- Wait 20–30 minutes before restoring full flow and skimming, giving the coral time to capture and begin digesting the food.
Feeding with pumps running full-blast is one of the most common mistakes — the food gets blown off the polyps or pulled into the skimmer before the coral can use it.
Broadcast vs. Target Feeding
Broadcast feeding — dosing food into the water column with flow reduced but still running — benefits filter-feeding fish and passive feeders across the tank. Target feeding is the better choice specifically for LPS like Acans, since it delivers food precisely to the polyp instead of hoping the coral captures passing particles.
For context, this is also why Acans differ from SPS corals like Acropora kept in the same system: SPS need finer, phytoplankton-scale food along with more light and flow, while LPS like Acans can take much larger meaty particles and prefer noticeably less light and flow. If two corals in the same tank seem to want opposite conditions, that's usually why.
Placement and Aggression
Acans carry sweeper tentacles and are semi-aggressive — they can sting neighboring coral tissue within reach. Exact "sting radius" claims vary across sources (anywhere from an inch to several inches), so it's safer to plan conservatively: leave at least 4–6 inches of clearance between an Acan and any other coral colony, including new frags you're placing nearby.
Good placement spots:
- Lower rockwork ledges, especially shaded ones
- A sandbed, mounted on a frag rack or plug
- Away from the direct output of any powerhead
Avoid stacking Acans directly beneath faster-growing corals that will eventually close the gap, and don't place new frags close to established colonies — stings from sweeper tentacles cause tissue recession on both sides of the encounter.
Tank Size and Compatibility
Acans can be kept in nano tanks starting around 5 gallons (19 L) if light and flow are dialed in carefully, though 10+ gallons (38+ L) gives more parameter stability and more room to space colonies apart from each other.
They pair well with peaceful reef fish — clownfish, gobies, and blennies are common tankmates — and with other low-aggression LPS. Avoid fish known to peck or nip at LPS polyps, including some butterflyfish and triggers, and be careful placing Acans next to other semi-aggressive LPS like torch, hammer, or frogspawn corals without adequate spacing. Browse the LPS coral selection if you're planning out a mixed LPS display.
Acclimating a New Acan
Corals shipped from lower-light farm or holding systems can be shocked by a display tank's full-intensity light and flow. Acclimate gradually:
- Start the new frag or colony at lower light and lower flow than your tank's mature settings — either a shaded, lower position or a temporarily dimmed fixture.
- Watch polyp extension daily over the first 1–2 weeks.
- Increase light and flow incrementally as the polyps stay open and extended, rather than jumping straight to your display's normal settings.
Skipping this step is one of the most common reasons a newly purchased Acan stays closed for days or bleaches shortly after introduction.
Troubleshooting a Closed, Pale, or Receding Acan
| Symptom | Likely Cause | What to Check |
|---|---|---|
| Polyps stay tightly closed | Too much light or flow, or recent move | Reduce direct light/flow; allow days to re-open |
| Pale or bleached tissue | Excess light exposure | Move lower/shadier; check PAR at that spot |
| Tissue recession near one edge | A neighboring coral's sweeper tentacles | Check clearance; move colony 4–6 in (10–15 cm) farther away |
| Small, dull polyps despite surviving fine | No supplemental feeding | Begin 2–3x/week target feeding |
| Algae or cyano film on tissue | Nutrient creep, not lighting | Check nitrate/phosphate trend and water-change schedule |
| Flatworms or pests on/near colony | Overfeeding residue, not lighting or flow | Inspect closely with a flashlight; distinguish from stress-related closure |
When multiple symptoms overlap, work through them in order: lighting and flow first (since these cause the fastest visible reaction), then spacing from neighbors, then feeding consistency, then nutrient export. This order usually isolates the real cause faster than adjusting everything at once.
A Note on Fragging
Fragging an Acan is a secondary but common task once a colony grows large. Cut between polyps along the natural skeletal ridges with a coral bandsaw, a sharp blade, or bone cutters — never through the center of a polyp or its mouth. Dip cut edges in an iodine-based coral dip to guard against infection, then glue the frag to a plug with cyanoacrylate or two-part epoxy. Keep new frags under lower light and gentler flow than the parent colony until the cut edges heal and polyps extend normally again.
Frequently Asked Questions
Are Acans easy for beginners?
Yes. Acans are generally rated as one of the hardier, more forgiving LPS corals, and they tolerate a range of parameters as long as changes are made gradually rather than abruptly.
Do Acans need to be fed, or is light enough?
Light alone can keep an Acan alive, since most of its energy comes from photosynthesis. Regular target feeding isn't strictly mandatory, but it visibly improves growth, coloration, and polyp extension, so it's strongly recommended.
What PAR/light level do Acans need?
Roughly 50–100 PAR is a safe general target. Acans can tolerate lower light without issue, and too much light causes bleaching and polyp shrinkage rather than faster growth.
How much flow do Acans need?
Low to moderate, and indirect. The goal is enough movement to prevent detritus buildup on the polyp surface without blasting the coral with direct pump output.
Can Acans sting other corals?
Yes, via sweeper tentacles that extend beyond the visible polyp. Keep at least 4–6 inches (10–15 cm) of clearance from neighboring coral colonies to avoid tissue damage on either side.
How often should I feed my Acan coral?
About 2–3 times a week with meaty foods like mysis shrimp or chopped seafood is the common recommendation, though a well-lit, established colony can often get by on once a week.
What size tank do Acans need?
Acans can work in nano tanks of 5 gallons (19 L) or more if light and flow are properly dialed in, though 10+ gallon (38+ L) systems offer more parameter stability and easier spacing between colonies.
Why is my Acan not opening or staying closed?
This usually points to one of a few causes: too much light, too much direct flow, unstable water parameters, recent shipping or relocation stress, or a nearby coral stinging it with sweeper tentacles. Check each in order, starting with light and flow since they tend to have the fastest visible effect.
Ready to add an Acan to your reef? Browse LPS hard corals on FishyHub, and pair your new colony with a suitable frozen or freeze-dried food for target feeding.
