dizzyf

Should I be worried about a greyish slug I saw in the tank? I can't find a picture of it on the internet, but it definitely wasnt black with a white stripe.

beachcomber

Do you have corals? Some slugs may eat them. If you don't have corals and the slug is not multiplying, it's probably ok for now. It might be a good member to the cleaning crew, but keep a eye on it.

pepetj

That depends on the slug species as well as the set up you have. I believe some sea slugs are safe even for reef tanks. Some are OK while alive but can foul a tank if they die and go unnoticed. Others are a major threat to keep.

I suggest you place activated charcoal as precaution in case it dies (as to neutralize or at least ameliorate the sudden release of potentially toxic molecules in the water column) while you find it and identify it. It usually take me some time to get some useful pictures of my tank inhabitants.

Pepetj
Santo Domingo

Goldwing_Don

Pictures are a must!

charzar-g

prehaps if its simply grey it might mean its a baby
I'm not sure - i haven't ever kept a slug, but keep an eye on it non the less