Setting up 20L

I went to Petco... couldn't stay away.. 20L tank for $20.. Can't beat that! I went right after work, I work in a small LFS, not a big chain. I got everything expect a heater and a light. I have it set up and running, temp sitting at 76, warmer then my room, which is 67.

I have my 4 yr old Penguin 200 running on the tank and I decided to put my 5" Female BN into the tank from the 37. I just did that, I know bad idea, but I just finished testing my water.

I'm shocked about the results, waited 5 mins: Ph: 7.4 Ammonia: .25-.50 PPM Nitrite: 0PPM(HOW, it stayed a light blue no change in color) Nitrate: 5-10PPM

That was before I put the BN into the tank. I'm guessing a W/C tomorrow. I don't use Prime or anything.. I have Well Water... Been using it for years never treated it and I had Angels breed non stop.

Never had Ammonia and Nitrates in my water. I do have a well seeded filter on the tank to cycle it faster. Could that cause the nitrates to appear instead of the Nitrite? I test my other tanks and no ammonia in them and low nitrates of only 10PPM.

I tested it before. Ph was 7.4, ammonia 0ppm, nitrite 0ppm and nitrate 0ppm. None of my tanks show ammonia, just the new tank. Everything is new expact the filter.
The filter used to be on my 37g which is decently stocked. From what I read Ammonia always shows up in new tanks even with an old seeded filter.

Still going to wait a bit to add more stock. Still need the light and heater.