Why Is My Torch Coral Not Extending? A Diagnostic Guide

A torch that will not open is the most common message we get about a single coral, and the honest first answer is that closed polyps on their own tell you almost nothing. A torch can be balled up tight for four days and be perfectly healthy. It can also have its tentacles out while a head quietly dissolves. What separates the two is not the polyps. It is the skeleton.

Why is my torch coral not extending?

In roughly that order: flow that is too direct, a recent change in light, nutrients bottomed out at zero, a neighbor stinging it, or a pest working on the tissue between the heads. Nine times out of ten it is something mechanical you changed in the last fortnight. The job is to work through the list in order rather than changing five things at once and learning nothing. One caveat worth stating plainly: nobody has published a ranked study of why aquarium torches close. The order below is our own judgment from running a facility full of Euphyllia, weighted by what is easiest to check and cheapest to reverse.

Before anything else: is there bare skeleton?

Look at the base of each head for white, exposed corallite where tissue used to be. If the tissue is intact everywhere, you have a husbandry problem and you have time to work through it methodically. If skeleton is showing and the boundary moves between photographs, you have a medical problem and it will not stop on its own.

What you are actually looking at

A torch “head” is one polyp sitting in its own tube of skeleton, called a corallite, typically 20 to 30 mm across. The visible coenosarc is the living tissue collar around each individual head and the skeleton immediately beneath it; it should not be pictured as a strap bridging separate branch tips. When that tissue begins to recede, damage often appears as a pale or white ring creeping up from the base of one head even while its tentacles still look normal.

Flow: the most common cause, and the easiest to fix

Torches want random, turbulent, indirect flow. A direct jet from a powerhead will keep a torch shut indefinitely and eventually damage the flesh, while dead-stagnant water lets detritus settle in the tentacles and invites infection. The tell is simple: if it opens at night when the pumps drop, or streams consistently to one side, flow is your answer. Be skeptical of anyone quoting you a specific velocity. There is no published flow figure for Euphyllia, and even the sources that disagree on intensity — Borneman says low to moderate, Top Shelf says moderate to high — agree completely on the type. Random beats strong. Move the coral before you touch the pump settings.

Light, and the finding almost nobody cites

Torches tolerate a wide band, roughly 50 to 200 PAR depending on which reputable source you ask, so the number matters less than the rate of change. A new fixture, a bulb swap, a schedule change or moving the coral up the rock will close a torch for days even when the endpoint is perfectly reasonable. A useful laboratory result needs careful framing here. Ben-Zvi, Eyal and Loya (2019) studied mesophotic Fimbriaphyllia paradivisa — a frogspawn relative, not Euphyllia glabrescens torch coral. Both treatments received extremely intense full sunlight averaging about 1,624 µmol m⁻² s⁻¹ of PAR; one treatment retained ultraviolet while the other filtered wavelengths below 400 nm. Within 24 hours, the UV-exposed polyps contracted and measured 73.1% smaller than the PAR-only group. That is evidence that UV can trigger rapid retraction in a related Euphyllid under extreme light. It is not proof that ordinary aquarium violet channels alone caused a closed torch, and the paper did not describe the contracted corals as healthy.

The practical consequence: if you changed lights and your torch closed, review both total intensity and spectrum instead of relying on one PAR reading. Shade the coral, reduce the total output, lower violet and UV channels, and ramp changes over weeks while checking for tissue loss, pests and flow problems. The study above used a different species and far more intense light than a normal reef aquarium, so treat it as a caution about abrupt exposure rather than a diagnosis. Our reef tank lighting guide covers the ramp schedule.

Nitrate and phosphate sitting at zero

An ultra-clean tank starves a torch. Aim for nitrate around 5 to 15 ppm and phosphate around 0.03 to 0.1 ppm. Undetectable readings on both, combined with pale color and stalled growth, is a recognized cause of retraction in Euphyllia and Goniopora specifically. This one has real science behind it, unlike the alkalinity folklore below. Phosphate starvation malforms the thylakoid membranes inside the symbionts, which raises their susceptibility to photodamage — which is why a nutrient-starved torch and a light-stressed torch so often turn out to be the same coral. See nitrate and phosphate target ranges for the full picture.

Alkalinity swings: what is actually known

“Euphyllia are alkalinity sensitive” is near-universal grower experience and is almost certainly describing something real. It has also never been quantified in a controlled study, and the numbers you will see quoted — more than 1 dKH in 24 hours, and so on — have no published basis for any coral, let alone this genus. The diagnostic value is real even if the threshold is not: an alkalinity event is a whole-tank event. If several unrelated corals sulked on the same day and it lines up with a dosing change, an ATO failure, a water change or a new test kit lot, chemistry is your answer. If only the torch is unhappy, it is not. Red Sea Reef Foundation Pro — Ca / Alk / Mg$79.99 · The three numbers a torch tank actually lives on

Is a neighbor attacking it?

If only the heads facing one direction are closed, you have a chemical or physical fight rather than a husbandry problem. Sweeper tentacles are modified, heavily armed tentacles that reach up to a foot and take around 30 days to develop, and they are usually deployed at night. Go and look after lights out with a torch before you blame your parameters. Two placement rules worth knowing. Hammers and frogspawn can often be arranged to intermesh safely with each other, but mixing E. glabrescens in with them is genuinely risky. And two torches of different genetic origin will develop sweepers against one another even though they are the same species, which is exactly what happens when people build a torch garden on one rack.

Euphyllia-eating flatworms

If recession is climbing from the base of a head while the tentacles above still look healthy, go looking for flatworms after lights out. They are the classic cause of exactly that pattern, because they eat the thin coenosarc tissue between and below the heads rather than the polyp itself. Adults are easy. They drop off within a few minutes in any standard coral dip. The eggs are the problem: on the newer variant they are described as so solidly attached that removal is near impossible even after months of desiccation. No dip is documented to kill flatworm eggs of any species, which is why the protocol is repetition rather than strength. Dip weekly for six to eight weeks. That interval is not arbitrary, though it is borrowed. The only published coral-flatworm life-cycle model we have is for the Acropora-eating flatworm, where at 27 °C eggs embryonate in 11 days and worms reach sexual maturity at 35 days. Weekly dipping catches every hatchling well before it can breed. It has never been validated on this worm, but it is consistent with the only real data in existence. Two Little Fishies ReVive Coral Cleaner — 500 ml$13.49 · What we run everything through before it enters our systems Dip in a separate container, never the display. Discard the dip water. Scrape the plug and the base of the branches where eggs concentrate. Quarantine new Euphyllia for four to six weeks if you possibly can. Full method in how to dip corals, and identification in coral pests 101.

Vermetid snails, the cause nobody checks

Look at the rock within a few centimeters of the coral for small hard tubes, and look at night for the mucus nets they cast. The net irritates whatever it lands on, keeping polyps retracted and eventually causing tissue loss. This is better evidenced than most hobby pest claims: a reef die-off study found a direct positive association between vermetid abundance and coral lesion counts, with vermetid-free colonies largely lesion-free. Retraction confined to one side or the base of a colony, with no flatworms visible, should send you looking for tubes. More in common reef tank pests.

Brown jelly, and what the paper everyone cites actually says

A brown gelatinous film with tissue disappearing underneath it is an emergency. Isolate the coral immediately, then baste the jelly off outside the display in a separate container and throw that water away. Blasting it in the tank inoculates everything downstream. This is the one step every source agrees on. Beyond that, be skeptical of confident protocols, including ours. Three corrections worth carrying:

What you will read	What the source actually says
“Helicostoma nonatum causes brown jelly”	Sequencing points to ciliates in the genus Philaster. The old name is an obsolete carry-over.
“Sweet et al. 2013 proved Euphyllia get brown jelly”	The Euphyllid in that paper was a white syndrome case. All three brown jelly cases were Acropora. The paper does not establish Euphyllia as a host.
“The ciliate is the cause”	The authors explicitly decline to say, offering two competing hypotheses. The ciliate may well be a secondary invader.

On dips, the often-quoted 1.5% potassium chloride figure comes from a controlled study on Goniopora where it killed the ciliates with 100% coral survival, and beat hydrogen peroxide, which stressed the coral. The concentration is evidenced. The immersion time everybody quotes is not — the paper never states one. Whatever you use, keep it brief and rinse in clean tank water. Whether to amputate is genuinely contested, and the tension is real: because the polyps are connected internally by gastrovascular canals, cutting is a bet that the infection has not already traveled past your cut — while injury itself is known to promote this class of disease. Growers who cut early and generously report better outcomes. Growers who cut report the trauma sometimes seeds a new lesion. We cut, and we cut early. Avoid the stacked antibiotic protocols on the forums. Mixing ciprofloxacin, amoxicillin and an algaecide has no rationale, no validated dosing, and is a good way to lose a colony and wreck your biological filter at the same time.

Where to cut, if you have to

Cut between polyps and as far below the head as you can get, into bare skeleton, well clear of living tissue and the coenosarc bridge. For disease the rule is different from ordinary fragging: cut ahead of the lesion into healthy tissue with a margin, not at the visible boundary. Use freshly mixed saltwater dosed with iodine to a light amber as the cutting bath, rinse loose flesh off afterwards, and keep the coral submerged until the polyps retract before you handle it. None of this applies to wall-form hammers and frogspawn. They have no branches, so there is nothing to cut between.

How long until it opens again?

If the cause was	Expect improvement in
Mechanical — flow, placement, a neighbor, a pest removed	Days
Chemical — light, nutrients, alkalinity	Two to six weeks
Nothing has changed after six weeks	You have not found the cause yet

That is facility experience, not published data — no one has measured torch recovery times. Photograph the coral from the same angle daily while you work through it. A tissue line that holds still is a coral sulking. A line that moves is a coral you are losing.

Related. If the torch arrived like this rather than declining after months in your tank, the cause was probably decided before it reached you. Why the cheapest coral costs the most explains what happens to a torch between the reef and a shipping box.

Before you buy the next one. What torch coral names actually mean covers how to read a torch listing photo and what to check before you spend.

The Underwater Gardener grows aquacultured corals in Key West, Florida (FL Aquaculture Certificate #AQ0254072). Our corals are raised under stable reef lighting in our own systems, so they arrive already adapted to a well-run tank. Corals ship UPS Next Day Air every Tuesday and Wednesday.

Why ours tend to settle faster

We grow our torches in Key West, in our own systems, under stable reef lighting, and we do not sell a piece that has been through a transshipper the week before. Most have never left the building until the day they are packed. That does not make them immune to a bad placement or a UV-heavy fixture, but it does mean the coral arriving at your door has one adjustment to make rather than four. TUG Toxic Green Aquacultured Torch$119.99 · Grown here, not collected. A forgiving first torch. 24K Gold Torch$249.99 · WYSIWYG. The piece in the photo is the piece that ships. All torches in stockEvery one photographed under known lighting, with placement notes