How Fast Do Acan Coral Grow? Growth Rates and Tips for Better Color
Acan coral is a slow-to-moderate grower, typically adding 1–3 new polyp heads per year in a stable tank, with well-fed colonies sometimes pushing 1–2 new polyps per month. Growth and color quality are closely linked, so the fastest path to a bigger, brighter colony is the same checklist: stable parameters, the right light and flow, and consistent feeding.
What "fast" actually means for Acan coral
Acans (a common hobby name that covers Acanthastrea, Micromussa, and related large-polyp stony corals) are not built for speed. Compared to branching SPS corals that can add visible growth in weeks, Acans measure progress in months and years.
A realistic baseline:
- 1–3 new polyp heads per year for a stable, moderately cared-for colony
- 1–2 new polyps per month, occasionally a new head every 2–4 weeks, in optimized, heavily fed setups
- 1–2+ years for a small frag to become a full 4–6 inch (10–15 cm) dome
You'll sometimes see claims of a "new head every 1–2 weeks." That figure almost always describes an already-mature, well-established colony budding off an existing head — not the pace at which a whole colony expands from scratch. Use the slower numbers above as your baseline expectation, and treat faster reports as the ceiling, not the norm.
New frags: expect a quiet phase first
A freshly cut or newly purchased frag often shows little to no visible growth for the first 1–6 months. That's normal. The coral is healing cut tissue and re-encrusting its base onto the plug or rock before it puts energy into expansion. Growth picks up noticeably once the base tissue has fully covered the mounting surface — judging a frag's progress before that point usually just leads to unnecessary parameter-chasing.
The core growth and color checklist
Acan growth and color come from the same set of conditions. A colony that's stressed, underfed, or over-lit rarely grows well even if it survives.
Feeding: the single biggest lever
Target-feeding meaty foods is repeatedly the difference between a stagnant Acan and an actively budding one. Feeding 2–3 times a week with items like mysis shrimp, brine shrimp, krill, or a coral pellet/powder food is commonly associated with roughly 30–40% faster tissue expansion and polyp budding compared to light-only (photosynthesis-only) colonies.
Practical feeding notes:
- Feed after lights dim or at night, when polyps extend and tentacles are most active
- Turn off flow for about 15–20 minutes while feeding, then restore it — this keeps food on the coral instead of blasting it away
- Don't overfeed; leftover food rotting on the tissue causes irritation and can invite infection
- Shrimp-based foods carry astaxanthin, a pigment tied to deepening reds, oranges, and pinks
Water parameters that support steady growth
Stability matters more than hitting an exact number. Wide or frequent swings in alkalinity and temperature stunt LPS growth far more than being a point or two outside the "ideal" range.
| Parameter | Target range | Note |
|---|---|---|
| Temperature | 76–82°F (24–28°C) | Stability matters more than the exact number |
| Salinity | 1.023–1.026 SG (~35 ppt) | |
| pH | 8.0–8.4 | |
| Alkalinity | 8–9 dKH (up to 12 dKH tolerated) | Tighter range is the safer, more consensus target |
| Calcium | 380–450 ppm | |
| Magnesium | 1,250–1,350 ppm | Supports calcium/alkalinity balance for skeletal growth |
| Nitrate | Under 10 ppm | Some detectable nitrate/phosphate is fine — see below |
Magnesium gets skipped in a lot of care guides, but it works alongside calcium and alkalinity to support skeletal deposition — worth checking alongside your other dosing.
Nutrients: aim for a sweet spot, not zero
It's tempting to chase "nitrate zero" as a goal, but ultra-low-nutrient systems can stall Acan growth and coloration just as effectively as excess nutrients do. Some detectable nitrate and phosphate actually support LPS corals better than a scrubbed-clean, ultra-low-nutrient tank. Treat nutrient control as finding a livable middle range rather than eliminating nitrate entirely.
Lighting for growth without washout
Acans want low-to-moderate PAR, generally in the 50–150 range, with many keepers finding 75–125 PAR a comfortable middle ground. Because tank spectrum and photoperiod both change how much PAR "feels" like to the coral, there's no single universal number.
- Start new frags or colonies at the low end (40–80 PAR), placed in a shaded or lower-tank spot
- Increase gradually while watching for bleaching, paling, or retraction
- Use a blue-leaning spectrum (roughly 20,000K) to intensify color
- Keep photoperiod around 8 hours of main lighting, with a ramp-up/ramp-down period
- Too much light doesn't speed up growth — it washes out color and can bleach tissue
Placement matters as much as intensity: put Acans in the lower-to-middle third of the tank, on rock or rubble rather than directly on sand. Sand grains can work into the coral's skeleton and irritate tissue over time; a raised frag rack works well if bare rock isn't available.
Flow: gentle sway, not direct blast
Acans prefer low-to-moderate, indirect flow — enough to deliver food particles and clear away mucus and debris, without closing the polyps up. Avoid pointing a powerhead directly at them. If flow is too strong, you'll typically see the coral stay retracted rather than fully extended, which limits both feeding efficiency and growth.
Placement and spacing
Give each Acan at least 2 inches (5 cm) of buffer space from neighboring corals. Acans carry sweeper tentacles that extend and sting at night, and a colony that's expanding outward can eventually reach a neighbor it wasn't near when first placed.
Fragging Acans
Once a colony has enough heads to spare, fragging is straightforward: cut between polyp heads using a bandsaw, coral cutters, or even a hacksaw blade, since each head is capable of surviving independently. After cutting, expect the same healing-and-settling lag described above — new frags need time to encrust before visible growth resumes, so don't judge a fresh frag's health by growth rate in the first few weeks.
Acan vs. Micromussa: does the name matter?
Many corals sold as "Acans" in the hobby have been reclassified as Micromussa lordhowensis under current taxonomy, alongside true Acanthastrea species. In practice, care requirements are essentially identical across these large-polyp stony corals, so don't over-index on the exact species label on a tag — the growth and color guidance in this article applies across the group. If you're shopping, FishyHub's LPS hard corals selection covers Acans and their close relatives together.
Buying tips: color under different lighting
Retail tanks often run actinic-heavy or blue-shifted lighting that makes corals pop in ways a home tank's spectrum won't replicate exactly. Expect some color shift after a new Acan acclimates to your lighting — this isn't a sign of stress by itself, just a difference in spectrum. Give a new specimen several weeks before deciding its "true" color under your setup.
This same spectrum effect matters when tracking your own coral's progress: photographing a colony under different lighting settings, camera white balance, or time of day can make color look like it changed when the actual pigment hasn't shifted at all. For a more reliable comparison, take reference photos at the same time of day, same camera settings, and same point in the light cycle each time.
Common mistakes to avoid
- Feeding without cutting flow first — leftover food rots on the tissue and causes irritation or infection. Turn pumps off briefly, feed, then restore flow.
- Ramping light or flow too fast on a new frag — causes retraction, bleaching, or failure to open. Increase gradually over days to weeks.
- Placing directly on sand — grains work into the skeleton and irritate tissue; use rock or a raised frag rack.
- Panicking over a closed or deflated Acan — this is common after transport, an alkalinity swing, or a lighting change. Give it 24–48 hours of stable conditions before assuming the worst.
- Ignoring spreading white or pale patches — these can signal rapid tissue necrosis or a bacterial issue. Isolate or frag away affected tissue and address it promptly rather than waiting to see if it resolves on its own.
- Judging growth too soon — new frags can look static for months. Consistency in parameters matters far more than frequent tweaking.
It's also worth remembering that a newly set up or still-maturing tank (before the biological filter is fully established) tends to produce slower, less predictable LPS growth regardless of how well you dial in feeding and light — patience with a young tank pays off as much as patience with a young frag.
Frequently Asked Questions
How long does it take an Acan frag to grow into a full colony?
Typically well over a year — often 1–2+ years to reach a several-inch dome. The first few months usually show little visible change while the frag heals and encrusts onto its base.
Do Acans need to be fed to grow well?
Not strictly, since they're photosynthetic and can survive on light alone. But target-feeding meaty foods 2–3 times a week is the single biggest lever for faster growth and noticeably better color.
What lighting is best for Acan color?
Low-to-moderate PAR, roughly 50–100, with a blue-leaning spectrum around 20,000K. Too much light washes out color and can bleach the coral rather than improving it.
Why is my Acan not growing or opening?
Usually unstable alkalinity or temperature, too much flow or light, or a recent move that hasn't been fully acclimated to. Stabilize parameters, avoid rescaping, and give it time before making further changes.
Can Acans be kept on sand?
Not ideally. Rock or a raised frag rack is preferred, since sand can work into the skeleton and irritate the tissue over time.
What's the difference between Acan and Micromussa coral?
Largely a naming and taxonomy issue in the hobby — many corals sold as Acans are classified as Micromussa lordhowensis. Care requirements are essentially the same across both.
How do I get my Acan to turn a deeper red or green?
Consistent feeding of shrimp-based foods (for the astaxanthin pigment) combined with stable alkalinity and moderate, not excessive, lighting tends to produce the deepest, most saturated color.
Is Acan coral good for beginners?
Generally yes. It's a moderate-difficulty coral that tolerates a range of light and flow conditions, and mostly rewards stability and patience over expert-level reefing skills.
Ready to add an Acan to your reef, or looking for the right target-feeding foods to support growth and color? Browse FishyHub's corals and freeze-dried foods to find what fits your tank.
