Yes a water change would take some of the nitrites out of the water, a very very small price to pay if you risk the chance of a cycle stall. The bacteria that converts ammonia to nitrite is mainly inside the filter, ammo bacteria can convert ammo to nitrite VERY quickly once theyve started to establish. You may add half a day to your cycle, Its insignificant.
Obviously a kh tester would be good to have but its nothing to cry and run to your 24hr walmart for this far into tank setup.
I dont know how it came across and im not going to argue with the science you put before me today, but quite frankly thats another science lesson altogether and not something to explain the cycles ins and outs to a beginner with their first tank. I was simply putting her at ease that she wont kill her cycle by not having a kh tester. And she wont
That even assuming she even has low kh.