I'm currently doing a fishless cycling and I'm approaching the end of my 3rd week. Ammonia has been great; now I can dose up to 4ppm and it'll be gone in less than 24 hours. I started seeing Nitrites at the start of the 2nd week. It's been gradually increasing and at one point it was off the charts, so I did a 50% pwc at the start of the third week. It reduced nitrites to about 0.50ppm, but then it started to increase again. Three days after the pwc I did another wc but this time 90%. Before I did the wc, the test for nitrites was off the chart again. One hour after I was done with the 90% wc the nitrites is still high at around 5ppm. Today the nitrites is still at the same level, it seems like it's not going down at all.

At the same time my Nitrates midway through my 2nd week and it skyrocketed until a point where a 50% pwc only brought it down to 80ppm. Finally a 90% wc brought it down to 10ppm.

It's a bit strange that the nitrites refuse to go down at all. Even after a pwc and a major wc. Any ideas why? Anyone can give any suggestion to help reduce the nitrites?

Thanks

Thanks for the help guys.

One final question. Should I do a water change so I get the nitrite within reasonable range or I should just add the platies?

eliminate any type of shark, you'd probably be okay