How Fast Do Acan Corals Grow? What to Expect

Q: My Acan coral doesn't look like it's grown at all — should I be concerned?

Not necessarily, especially over short timeframes — given how gradual Acan growth typically is, a lack of visible change over days or even a few weeks is common and doesn't on its own indicate a problem. The more useful question is whether the colony shows signs of stress or decline rather than just slow growth — the kind of distinction covered in our guide to telling if corals are stressed or unhealthy, which focuses on things like polyp extension, coloration, and tissue condition rather than growth rate specifically. A colony with good polyp extension, stable coloration, and no tissue recession that simply isn't visibly larger from one week to the next is most likely just growing at its normal slow pace — comparing photos taken months apart is generally a more useful way to assess growth than day-to-day observation.

By Hektor Jorgo Published December 24, 2024 Updated June 14, 2026 3 min read

A colony of Acan (Acanthastrea) coral with large fleshy polyps in a reef aquarium

Quick Facts

What Acan Coral Is: A large-polyp stony (LPS) coral genus (Acanthastrea) known for large, fleshy, often brightly colored and patterned polyps
General Growth Rate: Generally described as a slow-to-moderate grower compared to many LPS corals — new polyps appear gradually rather than rapid colony spread
How Growth Happens: New polyps typically bud off from existing ones (a form of asexual reproduction), gradually increasing the polyp count in a colony
Timeframe: Visible changes (new polyp buds, size increases) are often discussed in terms of months rather than weeks
Lighting: Moderate lighting is typical, similar to other LPS corals — very intense lighting isn't necessarily better for growth
Feeding's Role: Like other LPS corals, target feeding is commonly associated with better growth and coloration over time
Water Chemistry: Stable alkalinity and calcium, the building blocks of coral skeleton, support steady growth — the same parameters discussed for LPS corals generally
Patience Is Normal: Slow visible progress doesn't necessarily mean a problem — comparing photos over months, not days, is the more useful way to track growth

Acan corals are some of the most visually striking LPS corals in the hobby — large, fleshy polyps in dramatic colors and patterns. They're also a good reminder that "striking" and "fast-growing" aren't the same thing.

Short Answer

Acan corals (Acanthastrea) are generally slow-to-moderate growers compared to many other LPS corals, similar in pace to other large-polyp corals covered in our LPS corals for beginners guide. Growth typically happens through new polyps budding off existing ones, gradually increasing a colony's polyp count over time rather than rapid spreading. Visible change is usually a months-long story, not a weeks-long one — a colony that looks the same week to week is most likely growing normally, not failing to grow.

How Acan Growth Actually Happens

Rather than spreading outward as a sheet the way some encrusting corals do, Acan colonies typically grow by budding new polyps from existing ones — a form of asexual reproduction that gradually increases the total number of polyps in a colony. This is a slow, incremental process. The same general mechanism — budding new polyps from existing ones — is shared across several LPS corals, including Duncan corals and many brain corals, though the exact pace and pattern vary by genus.

What Affects Growth Rate

The same general factors that affect LPS growth broadly apply to Acans:

Lighting — moderate lighting is typical, similar to our LPS corals for beginners guide; very intense lighting isn't necessarily better and can sometimes cause stress rather than faster growth
Water chemistry — stable alkalinity and calcium supply the building blocks for skeletal growth, the parameters covered in our reef water chemistry guides
Feeding — target feeding (covered in our target feeding guide) is commonly associated with better growth and coloration for LPS corals generally
Overall stability — a colony dealing with ongoing stress (water quality swings, lighting changes, nearby irritants — the kinds of issues covered in our Kenya tree coral guide for a different coral) is less likely to show steady growth

Tracking Growth: Months, Not Days

Given how gradual Acan growth typically is, comparing photos taken months apart is far more useful than day-to-day observation. This is the same general timeframe discussed in our how long do corals live guide for coral longevity — slow, steady processes that don't show up on a daily timescale. None of this is unique to Acans; LPS growth generally tends to be a slower, polyp-by-polyp process compared to the faster lateral spread sometimes seen in chalice corals or certain soft corals.

"No Visible Growth" vs. Actual Decline

If an Acan coral doesn't look bigger from week to week, the more useful question isn't growth rate — it's whether the colony shows signs of stress or decline at all. Our guide to telling if corals are stressed or unhealthy covers the relevant signs: polyp extension, coloration, and tissue condition. A colony with good polyp extension, stable coloration, and no tissue recession that simply isn't visibly larger is most likely growing normally — just slowly.

Quick Reference

Acan corals are generally slow-to-moderate growers compared to many LPS corals
Growth happens mainly through new polyps budding off existing ones
Lighting, water chemistry (alkalinity/calcium), feeding, and overall stability all affect growth rate
Track growth with photos taken months apart, not day-to-day comparisons
No visible weekly change is normal — focus on stress/health signs instead of growth rate
Good polyp extension, stable color, and no tissue recession indicate normal slow growth
Very intense lighting isn't necessarily better for growth and can sometimes cause stress

Frequently Asked Questions

How fast do Acan corals actually grow?

Acan corals (Acanthastrea) are generally described as slow-to-moderate growers compared to many other LPS corals — similar in pace to some of the other large-polyp corals covered in our LPS corals for beginners guide, though specific growth rates vary by individual colony and tank conditions. Growth in Acans typically happens through new polyps budding off from existing ones, gradually increasing the total polyp count of a colony over time, rather than the kind of rapid lateral spread sometimes seen in faster-growing corals. Because of this, visible changes are often measured in months rather than weeks — a colony that looks the same from one week to the next isn't necessarily failing to grow, it may simply be progressing at a pace that's hard to notice without comparing photos over a longer timeframe.

What affects how fast an Acan coral grows?

The same general factors that affect LPS coral growth broadly: lighting (moderate lighting is typical for Acans, similar to the lighting discussion in our LPS corals for beginners guide — very intense lighting isn't necessarily better and can sometimes cause stress rather than faster growth), water chemistry (stable alkalinity and calcium supply the building blocks for skeletal growth, the same parameters covered in our reef water chemistry guides), and feeding (target feeding, covered in our target feeding guide, is commonly associated with better growth and coloration for LPS corals generally, including Acans). Overall coral health and stability matters too — a colony that's dealing with ongoing stress (from water quality swings, lighting changes, or nearby irritants, the kinds of issues covered in our Kenya tree coral troubleshooting guide for a different coral) is less likely to show steady growth than one in stable conditions.

How does Acan coral growth compare to how Duncan corals or brain corals grow?

The general mechanism — budding new polyps from existing ones — is shared across several LPS corals, including Acans, Duncan corals, and many brain corals, though the pace and pattern can differ between genera. What's common across all of them is that growth tends to be gradual and is best tracked over months, similar to the timeframes discussed in our how long do corals live guide for coral longevity generally. None of these corals are typically compared to the faster lateral-spread growth sometimes seen in chalice corals or certain soft corals — LPS growth in general, including Acans, tends to be a slower, polyp-by-polyp process.

My Acan coral doesn't look like it's grown at all — should I be concerned?

Not necessarily, especially over short timeframes — given how gradual Acan growth typically is, a lack of visible change over days or even a few weeks is common and doesn't on its own indicate a problem. The more useful question is whether the colony shows signs of stress or decline rather than just slow growth — the kind of distinction covered in our guide to telling if corals are stressed or unhealthy, which focuses on things like polyp extension, coloration, and tissue condition rather than growth rate specifically. A colony with good polyp extension, stable coloration, and no tissue recession that simply isn't visibly larger from one week to the next is most likely just growing at its normal slow pace — comparing photos taken months apart is generally a more useful way to assess growth than day-to-day observation.

Sources & Further Reading

About the Author: Hektor Jorgo

Co-Founder & Marine Biologist

Hektor is a co-founder of Sea Life Planet and has kept reef and freshwater aquariums for over 15 years. He holds a background in marine biology and focuses on species care accuracy, water chemistry, and tank husbandry.