Bronze corydoras reddy gills

[JuiceBox52]

Also more importantly I apolgise, excitement over new tanks etc taking over, if nitrites don’t fall afte water change after test in 3 days what should I do

Just keep doing daily water changes until they go down.

 

[Willbacon23]

Just keep doing daily water changes until they go down.

Perfect thanks so much

 

[Tez_20]

Perfect thanks so much

Harlequins are a lovely fish and like those temps plus they come in different colours...regarding your high levels i suggest doing as @JuiceBox52 said as i did this with my large tank while it was doing a mini cycle for 3wks and also extra oxygen if you can as it will ease any stress levels your fish get.