OK, I've looked over your edited first post again. Several observations and thoughts came to me: on day 33 when you took your old media and started using a new filter - that's significant as I've seen other cases where the colonies did not necessarily just continue on from that point as one might hope, so they may have been set back to some extent at that point, making the thought that you are on day 48 not how your bacteria would see it.
Another curious thing is your stretch in there (days 40+?) where ammonia stayed at 1.0 and you didn't add any more. I guess we probably talked about that but it seems odd to me once again, almost making me wonder whether its something about reading the test result. I assume it must be some shade of light green on the api ammonia test, right?
But then right here at the end after the large water change, you seem to be processing ammonia again. In the late stages of fishless cycling if nitrates(NO3) are going up pretty quickly (as I see yours are) but things seem a bit weird, I feel the kickstart effect of a large water change is a good thing. Its almost as though you get a handy bit of practice on weekends for what your future weekends will be doing gravel cleans. I did quite a few of them in the late stages on our current tank (in my case I needed to repeatedly raise KH/pH because my KH was zero, and I'm aware that's not your case) and came to feel that the fresh 90% of water, with the recharge of 5ppm ammonia gave me a good look at how the processing was going.
I still think you are past your nitrite spike, given that series of 3.3 readings earlier, as hopefully the N-Bacs will have stayed alive through the filter change and that's why we do indeed see NO3 rising eventually after you add ammonia.
Does your ammonia test give you a clear zero when you test your tap water? Assuming your tap water has zero ammonia thats always a reassuring test to see that the kit can indeed give you a good indication of zero ammonia.
~~waterdrop~~
