Marine Tank Cleaning Crew: The Snails, Hermits, and Shrimp That Actually Earn Their Keep

A reef tank without a cleaning crew is a janitorial labor sentence. Within 90 days of stocking fish and corals, detritus accumulates in the sand, hair algae establishes on rocks, and uneaten food rots between rocks. A properly stocked cleaning crew (CUC in the hobby acronym) removes 80 percent of this work and stabilizes nitrate and phosphate. This guide covers the specific species worth stocking, the ratios that actually work in a 20 to 100 gallon reef tank, and the species that cause more trouble than they solve. The trap most new reefers fall into is buying a bagged cleaning crew kit which dumps a random mix without species balance.

What a cleaning crew actually does

The crew has four jobs, and each species specializes in one:

1. Glass and rock algae grazing. Snails (trochus, astrea, cerith, nerite) eat film algae, diatoms, and short hair algae.
2. Detritus removal. Hermits, micro brittle stars, and bristleworms (yes, those bristleworms) process uneaten food and waste.
3. Sand bed turnover. Nassarius snails and certain gobies stir the sand to prevent anaerobic dead zones.
4. Parasite and dead tissue cleanup. Cleaner shrimp pick parasites off fish, and they scavenge dead matter.

A single species cannot do all four jobs. Stocking a mix is the goal.

The reliable snail species

Trochus snail (Trochus histrio). The single best reef snail. Trochus eat film algae, diatoms, and short hair algae across glass, rocks, and equipment. They right themselves when knocked over (most snails cannot). They reproduce in established tanks. Stock 1 per 5 gallons. Cost: 4 to 6 dollars each.

Astrea snail (Astraea tecta). Conical shells, dedicated rock and glass grazers. They cannot right themselves and starve if flipped, which is a real problem in tanks with strong flow. Stock 1 per 3 to 5 gallons. Cost: 1 to 2 dollars each.

Cerith snail (Cerithium spp.). Sand and glass scavengers, nocturnal. They burrow during the day and emerge at night to graze. The most underrated CUC species. Stock 1 per 5 gallons. Cost: 2 to 3 dollars each.

Nerite snail (Nerita spp.). Aggressive algae grazers. They are climbers and often crawl out of open top tanks. They lay white eggs across glass and rock that do not hatch in saltwater (eggs need brackish water) so the eggs accumulate as cosmetic clutter. Stock 1 per 10 gallons. Cost: 2 to 4 dollars each.

Nassarius snail (Nassarius spp.). Sand bed scavengers. They bury in the sand and emerge for food. A 30 gallon tank with 6 to 10 nassarius keeps the sand turned and uneaten food cleared. They do not eat algae. Stock 1 per 5 gallons. Cost: 1 to 3 dollars each.

Turbo snail (Turbo fluctuosa). Large, powerful grazers that pull through hair algae outbreaks. They are bulldozers and knock corals off frag plugs. Use them temporarily to clean a green hair algae outbreak, then move them to a refugium. Stock 1 per 10 gallons during cleanup, 0 long term.

The reliable hermit crab species

Dwarf blue leg hermit (Clibanarius tricolor). Small, reef safe, peaceful. They scavenge detritus and clean rockwork. Stock 1 per 4 to 5 gallons. Cost: 1 to 2 dollars each.

Scarlet reef hermit (Paguristes cadenati). Slightly larger than blue legs, attractive red coloration. Reef safe with caveat: they kill snails for shells if empty shells are not provided. Always stock 2 to 3 spare snail shells per hermit. Cost: 4 to 6 dollars each.

Species to avoid

• White spotted hermit (Dardanus megistos). Reef destroyer. Eats coral.
• Halloween hermit (Ciliopagurus strigatus). Beautiful but aggressive predator.
• Sand sifting starfish (Astropecten). Sand bed depleter, slow starvation in 6 to 12 months.
• Brittle stars (green and red Ophiarachna). Large brittle stars catch and eat sleeping fish.
• Conch (Strombus gigas as juvenile). Looks fine in store, outgrows 50+ gallon tanks.

Shrimp worth stocking

Skunk cleaner shrimp (Lysmata amboinensis). Picks parasites off fish, scavenges, peaceful in pairs. Stock 1 pair per 40 gallons. Cost: 25 to 40 dollars each.

Peppermint shrimp (Lysmata wurdemanni). Sold as aiptasia anemone eaters. Real result: 60 percent of peppermint shrimp eat aiptasia, the rest ignore it. Buy a group of 4 to increase odds. Stock 4 per 30+ gallon tank. Cost: 6 to 10 dollars each.

Pistol shrimp (Alpheus randalli with goby partner). A symbiotic pairing with watchman gobies. The shrimp digs and maintains a burrow, the goby stands guard. Pistol shrimp turn over the sand bed and provide entertaining behavior. Cost: 15 to 25 dollars each.

Sexy shrimp (Thor amboinensis). Tiny ornamental shrimp that dance on anemones. Visual interest only, no cleaning role. Stock in groups of 5 to 8 per 20 gallons. Cost: 8 to 12 dollars each.

A practical CUC plan by tank size

Nano (10 to 20 gallons):

• 4 to 6 trochus
• 4 to 6 cerith
• 2 to 3 nassarius
• 3 to 4 dwarf blue leg hermits
• 1 skunk cleaner shrimp

Small reef (20 to 40 gallons):

• 8 to 12 trochus
• 4 to 6 astrea
• 6 to 8 cerith
• 6 to 8 nassarius
• 8 to 10 dwarf blue leg hermits
• 2 scarlet reef hermits
• 1 to 2 skunk cleaner shrimp
• 4 peppermint shrimp (if aiptasia is present)

Mid reef (40 to 75 gallons):

• 15 to 20 trochus
• 10 to 12 astrea
• 10 to 12 cerith
• 10 to 12 nassarius
• 15 dwarf blue leg hermits
• 3 to 4 scarlet reef hermits
• 1 pair skunk cleaner shrimp
• 1 pistol shrimp and yellow watchman goby pair

When to add the cleaning crew

A new reef tank is not ready for CUC for the first 4 to 6 weeks. The cycle must finish (ammonia 0, nitrite 0, nitrate measurable). Diatoms (brown film) appear at week 3 to 5 and that is the signal to add the first wave of trochus and astrea. Add cerith, nassarius, and hermits 2 weeks later. Wait 3 to 6 months before adding shrimp, which are more sensitive to fluctuating parameters.

Stock conservatively at first and add more as the tank biomass increases. An overstocked CUC starves once the algae is consumed. A correctly sized CUC stays alive on the biological production of the tank.

See our reef tank starter species guide for the livestock side, and aquarium algae types and fixes for the algae the CUC controls. The /methodology page documents our parameter protocols.

Frequently asked questions

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