Sorry if I am being slow. I (think) I understand the nitrogen cycle now, but would cycling explain why 2 different test brands give such different nitrate readings? One said >40ppm and the API one said 0. The high figure makes sense (it was a few days since the last water change and reduced after I did another), but zero doesn't.
Could the presence of nitrite disrupt any nitrate readings I get (i.e. they are wrong until nitrite is 0)?
