I want to take it off. I cant do it the default is @ I think.

Is there a way to disable it and enable it again some other time?

go to user cp --> edit options and scroll all the way to the bottom.

it is possible to disable it and enable it later.

when I click the blank prefix It makes it "@"

Well i'm assuming you know the answer to that already since now it is not a @
but yeah, what ezeth said, just change the @ to anything you want, or insert your own one at options

No I mean I want it to be a " " (space) but I cant

You have to set it to the blank character; "‎‎"

When I set it to blank character " " it makes it "@"

you can't take it off

You can take it off, on my main I had no prefix for a long time. Google it and copy it directly from a UTF table then.

" " is clearly not blank, that is a space...

Try a width non-joiner.

Open character map, then scroll all the way to the bottom. Go 32 lines up and you should see a Zero Width Non-Joiner, copy that.