for the most part the paint will not adhere to glass and it will never have direct contact with water as you are painting the out side of the tank. i have used both Krylon spry and latex roll on, in blue and black. the blue seems to help add more light or at least it seems to brighten it up more. but overtime bring out the color of the algae growing on the glass. the black seems to do the opposite but seems to bring out the color of the corals more.