This is a discussion on Coconut shells as breeding caves? within the Beginner Freshwater Aquarium forums, part of the Freshwater Fish and Aquariums category; -->
I've seen coconut shells being used as breeding caves in aquariums (on google images!) - can they be used safely in an aquarium or ...
Nope,I put it straight in after making it.I didnt see it leech any tanins.
Just remember to drill a couple of 4mm (approx) holes near the top to prevent any air-pockets building up inside (plus you can also use these holes to thread fishing line through to hold on any java moss if you like).