Astrea Snail
Astraea tecta
A tireless film-algae grazer — the catch is it can't reliably flip itself back over.
Difficulty: BeginnerCleanup crewReef-safe
The astrea snail (Astraea tecta) is a dedicated film- and hair-algae grazer with a distinctive conical, often ridged shell — it works glass and rock hard and is one of the classic reef cleanup snails. Its one real quirk: unlike a trochus, it can't reliably flip itself back over. Land it upside-down on the sand and it can starve, so give any stranded snail a nudge.
Care at a glance
| Adult size | Around 1 in. |
|---|---|
| Minimum tank | Any established tank; roughly 1 per 3–5 gallons. |
| Temperature | 75–82°F (24–28°C). |
| pH | 8.1–8.4. |
| Specific gravity | 1.023–1.026 (reef-standard ≈35 ppt). |
| Other targets | Standard reef calcium and alkalinity keep the shell healthy; like all inverts it has zero tolerance for copper. |
| Diet | Film algae, hair algae and diatoms on glass and rock (a herbivore — it won't scavenge detritus like a cerith). |
| Temperament | Peaceful and fully reef-safe. |
| Reef-safe | Yes — grazes algae, leaves corals alone. |
| Natural range | Caribbean / Western Atlantic. |
The fish store gets these wrong
Common myths, kindly corrected — no shame for having believed them.
- "Any snail can right itself." Not the astrea — it's notably bad at it. Trochus snails self-right; astreas often can't, so check for stranded ones.
- "Astreas eat everything." They're grazers — film and hair algae — not sand-bed detritivores. Pair them with a cerith or nassarius for the sand.
Before you buy
- A cycled tank with algae to graze; drip-acclimate; never any copper.
- A willingness to flip stranded snails right-side-up.
- A sand scavenger (cerith or nassarius) alongside for full coverage.
Signs something's wrong
A struggling invert is usually telling you about water quality, acclimation, or (for shrimp and crabs) a fresh moult — here's what to watch for:
- Upside-down on the sand — flip it back promptly (it can't, and will starve).
- Empty shell — died from an un-cycled tank, a swing, or copper.
Never
- Never leave one stranded on its back.
- Never add to an un-cycled tank, dose copper, or drop it straight in.
Common astrea snail questions
Can astrea snails flip themselves over?
Not reliably — this is their one real weakness. An astrea that falls onto the sand upside-down often can't right itself and will starve, so flip over any you find on their back. (Trochus snails, by contrast, self-right well.)
What do astrea snails eat?
Film algae, hair algae and diatoms off glass and rock. They're grazers, not sand scavengers — pair them with a cerith or nassarius to keep the sand bed clean too.
Are astrea snails reef-safe?
Yes — peaceful algae grazers that won't touch corals.
How many astrea snails do I need?
About one per 3–5 gallons as a starting point, matched to your algae. Don't overstock or they'll strip the tank and then starve.
Why did my astrea snail die?
Most losses are from being added to an un-cycled tank, a salinity swing, copper, or being left stranded upside-down. Cycle first, acclimate slowly, keep copper out, and flip stranded snails.
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:
- Pod Your Reef — Saltwater Snails for Reef Tanks — algae grazing, self-righting, size
- Top Shelf Aquatics — Clean Up Crew Species Guide — grazer role, stocking
Written and fact-checked by The Coralkin Team against marine-aquarist sources — if your astrea snail is struggling, it's almost always water quality, acclimation or a moult — 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 →