well the adapter may have its uses but i doubt it would be any good for aquariums because its for ordinary t5s not HO or VHO t5s as used on aquariums. basically without upgrading to a newer fitting this enables more effiecent t5 tubes to be used so you can swap a 40w tube for a 28w tube . some of the newer, cheap all in one aquariums use ordinary t5s already. but at the moment most of the aquarium tubes are vho or ho so if you were to use this adaptor on say an old 4ft t8 fitting you would only be able to use cormmercial tubes so warm white and cool white possibly some industrial colouered tubes if you knew where to find them.