That is a spawning mop they are using, when that was put in they only put a few eggs elsewhere. That other cory trying to get in on the action was a C42 "kristina" male, he did manage to "T" with the female a few times but he was very annoying and chased the simulatus males away. The simulatus male is the other colour varient of simulatus, they can have the line down the back as in the female or the triangle shape on their sides.