Open Brain Coral

Trachyphyllia geoffroyi

The fleshy open brain that sits on the sand — stunning colour, but keep the flow gentle.

Difficulty: Beginner–IntermediateLPS coral

The open brain coral (Trachyphyllia geoffroyi) is one of the most beautiful corals you can put on a sand bed — a free-living, brilliantly coloured fleshy brain that inflates into folds of neon red, green or rainbow. It's a beginner-friendly LPS with two firm rules: it lives on the SAND (not the rock), and it wants gentle, indirect flow — strong flow tears its delicate flesh.

Good to know: SAND placement (never rock); gentle indirect flow — strong flow shreds the flesh.

📊 What keepers actually ask: Bought for its colour; the recurring mistakes are putting it on rock (it belongs on sand) and too much flow (it won't inflate, or it tears).

Care at a glance

Colony / form	A single free-living fleshy brain (not attached); inflates large by day.
Lighting	Moderate — around 100–150 PAR. Colour holds best at moderate light.
Water flow	Low to moderate, INDIRECT — gentle water movement across it; strong or direct flow damages the flesh and stops it expanding.
Placement	On the SAND BED — it's a free-living coral with a rounded skeleton made to sit in soft substrate, not on rock.
Temperature	75–82°F (24–28°C).
pH	8.1–8.4.
Specific gravity	1.023–1.026 (reef-standard ≈35 ppt).
Other targets	LPS build a stony skeleton — keep alkalinity (≈8–11 dKH), calcium (≈400–450 ppm) and magnesium (≈1300–1450 ppm) stable.
Feeding	Largely photosynthetic; feed small meaty foods a few times a week (it opens a feeding mouth, often at night) to boost health and colour.
Growth & spread	Slow to moderate; stays a single (large) colony rather than spreading.
Natural range	Indo-Pacific.

Beginner-friendly, done right. A stunning, beginner-friendly LPS — provided you respect two things. It's a FREE-LIVING coral that belongs on the SAND BED (its rounded base is made to sit in soft substrate; on rock it can't sit right and sharp edges damage it). And its flesh is delicate: keep flow gentle and INDIRECT, because strong flow tears the tissue and stops it inflating. Moderate light, gentle flow, occasional meaty feeds, stable alk/Ca/Mg — and it becomes a centrepiece.

Keep those numbers steady. This coral's alkalinity, calcium and magnesium only keep it safe when they're stable. If one reads low, our free reef dosing calculator works out exactly how much to add for your water volume — and splits it safely over days.

Where does it go? Light, flow and placement make or break a coral. Our free coral placement guide shows the PAR, flow and tank zone this coral wants — and what else thrives in the same spot.

The fish store gets these wrong

Common myths, kindly corrected — no shame for having believed them.

"Put every coral on the rocks." Not the open brain — it's a free-living, sand-dwelling coral; on rock it can't sit properly and gets damaged.
"More flow keeps corals clean." For a Trachyphyllia, strong flow shreds the delicate flesh and stops it opening — keep flow gentle and indirect.

Before you buy

A sand bed to sit it on (not rock).
A gentle, indirect-flow spot; moderate light.
Stable alk/Ca/Mg; small meaty foods to feed it.

Signs something's wrong

A struggling coral is almost always telling you about light, flow or water — here's what to watch for:

Not inflating or staying small — usually too much flow (or a parameter issue); move it to calmer water.
Torn or receding flesh, exposed skeleton — flow too strong, or a water-quality problem.
Brown-jelly-like slime — an infection; act fast (remove affected tissue, improve water).

Never

Never place it on rock — it's a sand-dwelling coral.
Never give it strong or direct flow — it tears the flesh.
Never let alkalinity swing.

Common open brain coral questions

Where do you put an open brain (Trachyphyllia) coral?

On the sand bed — it's a free-living coral with a rounded skeleton made to sit in soft substrate. Don't put it on rock, where it can't sit properly and sharp edges can damage its underside.

How much flow does a Trachyphyllia need?

Gentle, indirect flow only. Its flesh is delicate, so strong or direct flow tears the tissue and stops it inflating — aim for soft water movement across it.

Is the open brain coral good for beginners?

Yes — it's a beginner-friendly LPS with spectacular colour, as long as you keep it on the sand, give it gentle flow and moderate light, and hold your parameters stable.

Do I need to feed my open brain coral?

It gets most of its energy from light, but it benefits from small meaty foods a few times a week (it opens a feeding mouth, often at night) — feeding supports its health and rich colour.

Why won't my Trachyphyllia inflate?

Usually too much flow — it needs gentle, indirect water movement to expand fully. Check that it's on the sand in a calm spot, and confirm your parameters are stable.

Sources & further reading

This guide was written and fact-checked against these authorities. It's honest, general guidance — not a diagnosis, and not a substitute for an aquatic vet or your own test kit:

Tidal Gardens — Trachyphyllia Open Brain Coral Care — sand placement, gentle flow, feeding
Reef Builders — Trachyphyllia geoffroyi Open Brain — beginner LPS, care
Reef Chasers — Trachyphyllia Care — light, flow, feeding

Written and fact-checked by The Coralkin Team against marine-aquarist sources — if your open brain coral is struggling, it's almost always a light, flow or water-chemistry issue — check those first and ask an experienced reefer. We never guess a care number.

🔬 Review status: team-written and fact-checked against cited sources · not yet reviewed by a marine vet. How we research & fact-check →

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