Lid question - small gap

[sonfahig]

Wanted some advice on the small gap here. It’s about little under an inch. There was not another way to construct the lid as the hanger of my refugium was in the way. Do you think this will be a problem with jumpy fish and if so any ideas to help address it?

 

[get-salty]

That gap is definitely an escape route.
I'd find some sort of plastic and cut to shape and glue it down.