What pH water hardness nitate nitrite amonia levels are best before you introduce delicate fish into an aquarium that you want to survive?

pH and hardness really depend on the type of fish that you want to introduce. I highly recommend researching the particular type of fish and their requirements for pH and hardness.

Nitrate, nitrite and ammonia levels should be at or near zero for most kinds of fish, though once again it is recommended that you research the kind of fish that you're planning on introducing.