If your water changes are frequent enough, you can increase the volume to 80 or 90% without issue. I agree with stopping the store-bought water and use your tap. test it to see if you're adding ammonia, nitrate, etc. to the tank with your new water. Keep dosing the prime. Get the ammonia down to below 1 ppm if at all possible. It may extend the time it takes to cycle, but will help your fish.
Mark
Mark