There's this tiny thing I occasionally see on the glass of the aquarium, it sort of looks like a teeny tiny snowflake? I'm thinking it must have hitchhiked in on some live rock I got. It's so small it's hard to get a good picture of it but I'll try if that would be necessary for an ID.

Could it be an asterina star? They're really small, fairly common starfish that can hitchhike on live rock.