Silicone

BLACK
Ideal Seal MS290 is the ultimate all round sealant and adhesive.
Non-toxic.
Will bond to dry or wet surfaces and will even cure underwater.

Aquarium grade silicone safe for fish - with appropriate curing time. 

JUWEL silicone is a high-performance silicone which was specially developed for use in aquariums.

Juwel Conexo Underwater Silicone is a high-strength, neutral-cure silicone sealant that is specially developed for bonding plastics to glass.
It can also be used on wet surfaces and underwater, making…