My best bet would to take it out in my opinion. You cannot tell whether or not that starfish is good or bad. I had tons of Astera Starfish (very similar to that) that nibbled relentlessly on my zoos and plays.
As for whats growing underneath your ricordea that harmless. Just an indication of how well your tank is coming along.
So the white stuff is nothing to worry about? Is it just an indication that the tank is maturing and it's a good thing, or could it be a bad indicator? Thanks for answering my questions