brown thing

Hey so I moved my snail (I think it’s a turbo) and hermit crab from my other tank into this one. I didn’t do an official QT, I just scrubbed the shells really well in a bowl of new + old tank water and then once really clean I dunked them separately in a new dish of RODI. I thought that would be...

What is this, there is something on my rocks and in the sand that has brown red tint and does not look normal.