Even when using existing filter media, or even an existing filter, your tank will still cycle. Using the existing biomedia will significantly reduce the duration and intensity of the cycle, but it will still occur.
A level of 1ppm ammonia is harmful and I would put in an additive for now to reduce the amount of ammonia in the tank immediately. The drawback of this is artificially neutralizing the ammonia slows down the cycling process, but it is better than losing fish.
If at all possible, I would remove the stock from the tank and cycle the tank with disposable fish or a fishless cycle.
A level of 1ppm ammonia is harmful and I would put in an additive for now to reduce the amount of ammonia in the tank immediately. The drawback of this is artificially neutralizing the ammonia slows down the cycling process, but it is better than losing fish.
If at all possible, I would remove the stock from the tank and cycle the tank with disposable fish or a fishless cycle.