Aquarium safe tile sealer?
Hi all. I'm a new user of this forum but I've been lurking for months soaking up info as I've been getting into this hobby. Great forum! Anyways, I plan on building a small betta aquarium of approximately 5 gallons from slate tile with a glass front. The slate is going to be the majority of the structure and will of course need to be waterproof to hold the water. I already know about GE #1 silicone to hold it together but need a product to seal the tile surfaces. Are any such products readily available for affordable prices? I've seen those old meta frame slate bottom aquariums and obviously they work, so there must be some product available.
If it helps, I actually have some commercial grade aliphatic moisture cure urethane on hand that I believe would do the trick of sealing the tile but I'm not sure it would be aquarium safe once sealed. I would prefer to use this product as I already have it and have experience working with it professionally, but if it won't work that's fine. I just need to know what will.
Thank you for reading and for any advice rendered!