Olive oil burns when you get it too hot.
Better to use a specific cooking oil. Canola, Peanut etc.
Also, have a shot at using a tempura batter for ya fish.
Any water added to make a batter should be ice cold. Then let the batter settle, before coating fish.
There are many ingredients for a successful batter.
s/r flour, plain. corn flour, custad powder for colouring, whisked egg white, beer and many more. Just gotta experiment to get what you like.
Cheers Phill