The answer for the question is very simple:)
give your textarea an ID
Old:
<div id='ckeditor_div' style='display:none;'><textarea class='ckeditor' style='display:inline-block;' name='tooltip_info'>". $tooltip['tip'] ."</textarea></div>
New:
<div id='ckeditor_div' style='display:none;'><textarea id='ckeditor' class='ckeditor' style='display:inline-block;' name='tooltip_info'>". $tooltip['tip'] ."</textarea></div>
as you can see i added id='ckeditor'
in the textarea