No no no, if this is done with cement/concrete, then I would never put this in a stocked tank. After it has been cured, I would stick it in another tank, with a filter (a sump would work best), and run the tank with salt water for 2-3 days. Do a full water change, and repeat this step once or twice more. Then empty the tank, put fresh water back into the tank, and circulate it again for 2-3 days and repeat again. Then start using media bags from a previous fish tank and get your cycle going again (of course testing your tank water) before adding the little guys n girls. This could be very harmful to your fish if not done right.
--edit-- don't use hot glue, use GE 1 Silicone