Test your containers with the store premixed water before you even use it. Not comfortable with your LFS but online and above post #12 good.Guess the problem is that there is living things in there, and Ive watched the ammonia to to nitrite and nitrate a couple times now... It has seemed to keep coming back even once I hit 0-0-40ish.
Have not used anything but the premixed RO salt mix from the store for changes since initial fill. Just when readings got good again and they said come back in 3 days if still good take the clown home... They get ammonia reading again.
While the clown (and any addition) always cause a little mini cycle increase, I agree with others your tank never had a chance to cycle. Water changes should target 1x weekly with 10% change. Give you tank a chance to rest.