First off I wanted to compliment you on your work. Very well done. I have one question though. Is the quikrete and titebond III going to release toxins into your water?
Thanks for the compliment. To answer the question no, once properly cured they both are safe. Quikrete has to repeated soaked and rinsed for a few weeks to neutralize its ph. This process can be expedited using vinegar or a mild acid. Some zoo exhibits and aquarium keepers actually use cement based products for their enclosures. The Titebond once dry is FDA approved for indirect food contact once cured, it just have to dry throughly which takes a couple of weeks. Ive used Titebond II which is weather proof not water proof, and I never had any problems with it breaking down or leeching so I figure Titebond III will hold up even better since there is a portion of it that would be submerged.