What media are you using, as in gravel, shell grit, rubble, base rock or what ever to house the bacterium’s?
If this is a QT you are setting up, then while it is not is use you should leave a little dead tissue in there always to keep the bacteria fed and active.
Just with ammonia, unlike ammonium it can disrupt PH, so that’s something to adjust before using your QT each time.
While dead tissue is there, it has absolutely no adverse affect on nitrites, they will develop and drop away no matter what you do if the bacterium’s are looked after and have a place to grow and thrive.
The reason most folks get parasites is from two issues, not enough protists and not enough varied bacterium’s! From each type of waste or dead tissue comes another slightly varied form of ammonia which requires a slight variation in oxidising bacteria for oxidation, near no one establishes all the needed variations at the start to enable near no ammonia to be present when introducing life each time, so until lots a varied bacteria are set up and thriving, protists that graze on your cyclers bacteria and use some for symbiotic purposes keeping ich and velvet at bay to some degree and are in large numbers, then the bio filter is not completely mature.