Another obvious chemical that won't affect the pool is muriatic acid. I wouldn't want to get sodium hydroxide or similar chemicals in any water I would get in. You can always refer to your MSDS sheets and instructions on your chemicals, if there are lots of precautions regarding pets, plants, and people, you probably don't want it in the water. I have always stayed with bleach if anything around a pool. Acid is fine for rust stains, etc.