Mark,
Thanks for posting the below info. It's reassuring to know the stuff is safe.
-Pat

The Great Stuff will work fine in your application. The surface area does
not need to be completely dry since the foam cures by absorbing moisture.
The cured foam is organic material so it will not harm the fish or plant
life in any way. If you have any further questions please let me know.
Regards,
Sean Ramballie