I'm confused Need help!

I am lost here. I thought I was finished with my fish less cycle. All the numbers were perfect. Ph was slightly down from when I started about 7.8
Nitrites finally came down to 0 nitrates were at .20 ppm and ammonia was 0 ppm. I read just prior to adding fish and completing your cycle to do a massive water change which I did. I changed 50 % of the water. Well I just tested the water about 2 hours after the water change and my nitrites are up between 2.0-5.0. Also I forgot to mention that my tap water is 7.4 ph 0 ammonia 0 nitrates and 0 nitrites. Why would nitrites show up after a water change. Could I be getting a false reading because I am testing the water too early. Should I have to wait a day to test after the water change. I'm lost because my nitrites went up and I don't know why or how.

When I did my cycle on my 180, I continued to add ammonia until I got 3 consecutive days of 0 ammo, 0 nitrites, and about 20 on nitrates.

Did you do a water change after the third day or just put fish in it.

Yates said:

Did you do a water change after the third day or just put fish in it.

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I did a 50% wc and started adding fish.
I kept checking water parameters daily for another week.
after that, I checked water parameters weekly for a few months.
nowadays, i check water parameters once or twice a month.
I do keep doing a 40% wc weekly.

Copy. I just don't understand how I could go from no nitrites to the spike of about 2-4 ppm with a water change. My tap water is 0 ppm. What would cause this.