I bought the tank with the fish, a few tetras, 2 BIG plecos, 2 kuhli loaches and the peacock eel. I was there when he emptied it.
I kept all the fish in a smaller tank to let it run for a few days because I added all the new water and wanted to test it to make sure everything was all right.
I rehomed the plecos because they were far too large for the 55 gallon tank and gave the tetras to my friend.
It's been closer to 2 weeks of having the fish in the tank, and because the tests were all good I bought a new kuhli loach.

I don't have the exact number but when I first tested the nitrates they were below what the directions said was safe, and then after the water changes I did they are now almost zero.