Aquarium Silicone Adhesive - Black 10 ounce
Aquarium Silicone creates lasting, strong and leak-proof bonds. The non-toxic silicone works great for all types of glass fish tank. If you need to repair your current tank, creating a new one, or you simply just have a project that you are working on look no further.
1x 10.2oz Tube Black Silicone
Note: Do not recommend for the use with acrylic
I would recommend using super glue and instant set and then covering the joints with Marco Mortar:
It sets fast and sets in water. In our rock scaping tests we found that it made a strong joint for the cost of materials.