Fiberglass resin maybe a better choice if used along with fiberglass fabric for added strength. It is commonly use for building large preformed fish ponds. Therefore it should be safe. It is also more flexible. Epoxy are very brittle once cured. Not all epoxy are fish safe. Liquid rubber may sound like a good choice but my experience with it is not good. Once it start to peel, you can not just do a patch job. The old and new surface will not bond to each other. Even repainting the whole thing sometimes will not work. Fiberglass resin can be sand down to allow the new coat to bond much better. It is much cheaper in cost and just about any pigment can be added. As alway, do more research. These are only based on my experience with the material used in the past.