So I've been cycling my indoor aquarium system for coming up to three weeks now.
Ammonia's sitting pretty low (0.25ppm) but I occasionally up it to 2-3ppm to make sure the nitrosoma bacteria don't starve.
Nitrite spiked about a week into the cycle, but hasn't some down. It's been showing about 5ppm ever since.
Yesterday I added some gravel from an established tank (the aquarium store were very helpful) and some
Today I decided to get a better idea of what the nitrates actually were. First I tried diluting by 10 times (0.5ml of tank water to 5ml) of tap water and tested that. Result was a slightly slower nitrite reading, but it still got to 5ppm after 5 minutes (indicating at least 25ppm really!).
Next, I tried diluting by 100 times (5ml tank water in 500ml of tap water). Finally a sensible reading: 0.25ppm, implying a real reading of 25ppm.
To confirm, I diluted by 50 times (10ml tank water in 500ml of tap water). This confirmed the result by showing 0.5ppm (again implying 25ppm).
I considered doing a water change to bring the nitrates down to a readable range (in case the high nitrites were inhibiting nitrospira bacteria) but I've decided to leave it a few days and see if I can measure any drop. If it doesn't drop at all I'll do a water change in the week. I'm worried about fiddling too much at this point...
So I guess my question is: is this normal? does it mean I over-dosed the ammonia at the start? Do you think waiting is the best option?
My tank is pretty cold (it's indoors but not heated) I'd guess about 15C but I'll measure it later. But the DO should be very high as I've got all sorts of pumps going

It's hard to tell if the nitrates have come from the bacteria as my tap water is high in nitrates (it's lower now than it was when I started cycling!).