Pool Party - S1-E2
Other mistake: After Cleo transforms into a mermaid, her wetsuit doesn't disappear for some reason.
The Gracie Code: Part 1 - S2-E19
Other mistake: Cleo explains how Emma found Gracie's locket at the bottom of the Moon Pool. Gracie's locket is the one that Cleo wears, meaning the stone it it is blue, but in the flashback of Emma discovering the locket, the stone is red.
Answer: No explanation was given as to why his character disappears. As to the actor who played him, Christopher Poree, this appears to be his only acting credit, and he retired as an actor following his time on the show. There is little online information about his personal or professional life and none that I could find on why he left the show.
raywest ★