Reef Cleanup Crew Stocking Guide: Who, What, How Many

The cleanup crew (CUC) is your reef's sanitation department: snails, hermits, and shrimp hired to eat the algae, detritus, and leftovers that would otherwise become nutrient problems. Stocked well, a CUC works silently for years. Stocked badly — usually by following the internet's wildly inflated "one snail per gallon" folklore — it becomes a slow-motion die-off that pollutes the tank it was hired to clean.

Here's who does what, how many you actually need, and the myths to ignore.

First, the golden rule: stock to the food supply

A cleanup crew is livestock, and livestock starves without food. Your tank grows a finite amount of algae and produces finite detritus; every janitor you add divides that food further. The classic beginner error is buying a big "cleanup crew package" for a young tank, watching the algae vanish in two weeks — and then watching the crew quietly starve, die in the rockwork, and feed the next algae bloom.

So: start with a small crew, and add more only if visible algae persists after a few weeks. You can always hire more janitors. You can't un-starve dead ones. And forget "per gallon" math — a lightly stocked 40-gallon with strong export grows less algae food than an overfed 20-gallon. The rates below assume a typical beginner tank in its first year; treat them as ceilings, not quotas.

The roster: who actually does what

Snails — the core workforce

• Trochus snails — the best all-around grazer: film algae, diatoms, some hair algae, on glass and rock. Crucially, trochus can right themselves when they fall — many snails can't, and an upside-down snail is a dead snail. Rate: 1 per 5–10 gallons.
• Cerith snails — small, tireless, and they work the sandbed as well as surfaces, eating film algae, detritus, and leftover food. They burrow, which keeps the sand surface turned. Rate: 1 per 5 gallons.
• Nassarius snails — not algae eaters at all: they're scavengers that live buried in the sand and erupt dramatically when food hits the water. They handle uneaten food and carrion — the pollution sources you can't see. Rate: 1 per 10 gallons; only for tanks with a sandbed.
• Astrea snails — enthusiastic rock grazers with one fatal flaw: they cannot flip themselves. Fine in small numbers if you're willing to be their rescue service. Optional.
• Turbo snails — algae-eating bulldozers. One turbo outgrazes five trochus, but they're big, clumsy (they knock over unglued frags), and one or two is plenty in a 30–40 gallon tank. Skip the Mexican turbo in warm tanks; it's a subtropical species that runs hot tanks poorly.

Hermit crabs — useful, with an asterisk

• Dwarf blue-leg and scarlet hermits — scavengers and algae-pickers that reach crevices snails can't. The asterisk: hermits are opportunists, and a hungry hermit will absolutely kill a snail for its shell, its meat, or both. Two mitigations: stock them sparsely (1 per 10 gallons), and scatter a handful of empty shells in assorted sizes so shell disputes get settled at the hardware store instead of by murder. Scarlets are the best-behaved; the bigger the hermit species, the worse the behavior.
• Some keepers run snail-only crews specifically to skip hermit politics — a completely valid choice.

Shrimp and specialists

• Cleaner shrimp — a scavenger with a show-business side hustle: it'll clean parasites off willing fish. One per tank; they're semi-territorial with their own kind. Not essential, universally beloved.
• Emerald crab — the bubble-algae specialist. Hire one if you have bubble algae; otherwise skip, as a bored emerald gets ideas.
• Fighting conch — a wonderful sandbed cleaner for tanks 40 gallons and up with a deep sand footprint.
• Skip entirely: sand-sifting starfish (they strip a sandbed's fauna, then starve), sea urchins in small tanks (bulldozers), arrow crabs and sally lightfoots (turn predatory), and any "assorted hermit" grab bag.

A starter crew for a 30-gallon tank

Concretely, for a typical 20–40 gallon beginner reef finishing its cycle and entering the diatom phase:

• 4–5 trochus snails
• 5–6 cerith snails
• 3 nassarius snails
• 2–3 dwarf hermits (optional) + spare shells
• 1 cleaner shrimp (optional, once the tank is a couple months old)

That's a modest $40–60 order that matches a young tank's food supply. Scale roughly linearly for other sizes, rounding down. Add the crew as the cycle ends and the first algae appears — they'll meet the diatom bloom head-on, which is exactly the timing you want.

Two care notes people skip: acclimate inverts slowly — snails and shrimp are far more sensitive to salinity swings than fish, making drip acclimation genuinely mandatory (our drip acclimation guide covers it), and verify your salinity with a calibrated refractometer before they arrive. And feed the crew in lean times — once your tank matures and algae thins, an occasional sinking pellet or algae wafer keeps the janitors from starving on the job.

What a CUC can and cannot do

A cleanup crew is maintenance staff, not a cure. It handles the daily film, grazes the rock, turns the sand, and cleans up feeding accidents. It cannot fix a nutrient problem — a tank growing hair algae faster than an army could eat it has an input problem (feeding, source water, export) that no invertebrate solves. And it doesn't replace your scraper: snails keep glass better, but the front pane stays truly clear because a magnetic algae scraper crosses it for sixty seconds every day or two.

Expect attrition, too: a few percent of the crew dying per year is normal (replace them), and empty snail shells don't always mean death — check whether a hermit upgraded its housing.

The full hiring guide — including CUC myths that refuse to die and the seasonal rhythm of restocking — is a chapter of our beginner's guide, The First Tank.

FAQ

How many snails per gallon do I actually need?

Roughly one snail per 3–5 gallons total, mixed across species — a fraction of the "1–2 per gallon" numbers that CUC package marketing suggests. Overstocked crews strip the tank in weeks and then starve, adding pollution. Start below the guideline and hire more only if algae persists.

Why do my snails keep dying?

Four usual suspects, in order: acclimation shock (inverts need slow drip acclimation and stable salinity), starvation (too many janitors, too little algae), hermit crabs (check for suspiciously relocated shells), and — in older tanks — slowly drifted salinity or alkalinity that fish tolerate but inverts don't. If new snails die within days, it's acclimation or water; if they fade over months, it's usually food.

Do I need a cleanup crew at all?

Strictly, no — a lightly fed tank with good export and a diligent keeper can run without one. Practically, a modest CUC does hours of your weekly maintenance for free, reaches places you can't, and converts leftovers into recoverable waste before they become dissolved nutrients. Almost every successful reef runs one; the trick is simply not overhiring.