Can someone confirm the good news?

I've been trying to cycle for almost 40 days without success. I decided to do a 90% WC last week to maybe start over. Well, today this was my reading of nitrites. The one on the left is my aquarium and the one on the right is my tap water. The tap water is absolutely 0 ppm. The one on the left doesn't look the same. Can someone confirm my cycle is underway?!

How are you cycling the tank?

When I last did a fishless cycle using ammonia, it took 7 weeks to finish.

essjay said:

How are you cycling the tank?

When I last did a fishless cycle using ammonia, it took 7 weeks to finish.

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I was using ammonia. It wasn't working. Completely stakes, and never got under way. I did a 90% WC and I am finally starting to see nitrites. Now I am doing a fish-in cycle with a platy. I am carefully monitoring ammonia though.

If there are fish in the tank you need to do a water change every time ammonia or nitrite read anything other than zero.

If there is one platy in the tank, enough bacteria will grow to deal with the ammonia made by that one platy, no more. When you add more fish, the bacteria will need to catch up so you may well find ammonia and/or nitrite showing up again. Keep an eye on the levels whenever you add more fish.

essjay said:

If there are fish in the tank you need to do a water change every time ammonia or nitrite read anything other than zero.

If there is one platy in the tank, enough bacteria will grow to deal with the ammonia made by that one platy, no more. When you add more fish, the bacteria will need to catch up so you may well find ammonia and/or nitrite showing up again. Keep an eye on the levels whenever you add more fish.

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But wouldn't doing a WC not allow the bacteria to grow?

The bacteria grow in the biofilm which is firmly attached to all the surfaces in the tank. As long as water conditioner is added to the new water to remove chlorine or chloramine, water changes will not harm the bacteria.
Even with zero reading, there will be traces of ammonia and nitrite in the water and this is enough to feed the bacteria so thatw they will multiply.

Not doing water changes risks damaging the fish, if not killing them.