Aquariums are made up of glass panes. The glass panes of an aquarium are not allowed to touch each other as they are subjected to vibrations from the water, fish tank pump, movement of the fish and transfer of vibrations from persons passing by. This can lead to damage of the glass. The thin layer of adhesive is not elastic or flexible to absorb all these forces that might occur and may result in cracking of the glass.
Apart from this UV adhesives are not completely waterproof and after sometime water might penetrate through the bonding area and the bonded surfaces might come apart.
Only special silicone based adhesives can be used for aquariums.
Silicone has very good adhesion to glass and is specially designed for aquariums an glazing construction. It locks the water and forms a durable seal that does not shrink or lose flexibility while drying or curing.