Chapter 7 starts the signs and wonders to show not just Pharaoh but all of Egypt and the Israelites who the Lord really was...Yahweh.
The magicians of Egypt were able to duplicate what Aaron did with the staff turning it into a serpent and then also turning water to blood by their secret arts. It doesn't say how that worked exactly but I don't believe it was good. It wasn't as powerful or controlled either. Their staffs got eaten by Aaron's and they couldn't change the blood back to water.