yes you can,you must get one suitable for aquariums
(fosroc,silaflex rtv glass & ceramics,clear)
get it from miter 10, bunnings, placemakers and so on
make sure it is dry,one drop of water is one leak
let dry,as a rule 1mm of silicone equals 1 day to dry,10mm = 10 days
use glove not bare skin finger