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Noticed a few small crabs in my Zoanthid colony today. They're tiny, maybe 3mm, but I'm worried they might mess with the polyps. Anyone dealt with these before? Tank's a 40-gallon mixed reef, parameters stable, 78F, salinity 1.025. Running a Radion XR15, weekly 10% water changes.

Those sound like commensal crabs, which usually don't harm corals. I've had them in my Acropora for years without issues. Check if they're picking at the polyps or just hanging out. If they're not causing damage, I'd leave them be. What's your nitrate level? High nutrients can sometimes make them more active.

troubadour wrote: ↑Fri Aug 01, 2025 11:18 am Noticed a few small crabs in my Zoanthid colony today. They're tiny, maybe 3mm, but I'm worried they might mess with the polyps. Anyone dealt with these before? Tank's a 40-gallon mixed reef, parameters stable, 78F, salinity 1.025. Running a Radion XR15, weekly 10% water changes.

I had a similar scare last month. Turned out they were just eating detritus. My Zoas actually opened up better after the crabs showed up. Maybe they're cleaning the base? What's your feeding schedule like?

Yep, most tiny reef crabs are chill. But if you're sketched out, try spot-feeding the Zoas at night. If the crabs ignore the food and keep picking at the flesh, then you might have a problem. My tank's got a bunch of these dudes, and they've never caused trouble. You running carbon or any chemical filtration?

Man, I freaked when I first saw these little guys too. Thought they were gonna wreck my Torches. Turns out they're just vibing. If they start looking sketchy, you can lure them out with a piece of shrimp in a bottle trap. But honestly, they're probably just part of the cleanup crew.

How do you tell if they're bad crabs? I've got some in my tank but don't know what to look for. My LFS said they're fine, but I'm still nervous. Tank's a 30-gallon with soft corals, no SPS. Parameters are good, 0 ammonia, 0 nitrite, 5 nitrate.

Thanks for the input, everyone. Nitrates are at 3ppm, so pretty low. I'll keep an eye on them and see if they bother the polyps. Might try the spot-feeding trick to check their behavior. Appreciate the help!

Savoye wrote: ↑Fri Aug 01, 2025 3:38 pm How do you tell if they're bad crabs? I've got some in my tank but don't know what to look for. My LFS said they're fine, but I'm still nervous. Tank's a 30-gallon with soft corals, no SPS. Parameters are good, 0 ammonia, 0 nitrite, 5 nitrate.

Look for black tips on their claws or if they're actively tearing at coral flesh. Good crabs usually have smooth, rounded claws and stay near the base. If yours are just crawling around without damaging anything, they're likely harmless. What's your lighting schedule?

Also, bad crabs tend to hide during the day. If yours are out and about, they're probably just scavengers. My tank's got a bunch of these little dudes, and they've never caused issues. You running a protein skimmer? That might affect their behavior if detritus is scarce.

Yeah, protein skimmers can cut their food supply. If you're worried, try reducing skimmer time for a bit and see if they calm down. But honestly, unless you see actual damage, I wouldn't stress. My crabs even help keep algae in check. What's your flow like? High flow can sometimes make them more active.