Many people on this forum have new tanks that aren't completely cycled or tanks that are over-populated with inadequate filters. Even so, nitrite spikes are common reasons to lose fish - maybe you had a power outage in the night and your filter bacteria died off, maybe your filter got blocked, but most commonly it's due to difficulties dealing with a new tank set-up and poor advice on stocking from LFS's.
Nitrate levels are a particular problem in parts of the world where nitrate levels in drinking water are not adequately controlled, but also as a hang-over effect from when a new tank was cycled with fish, due to plants dying in the recent heat-wave and due to over-stocking.
So it is extremely relevent to report nitrite/nitrate levels when trying to solve a fish death mystery, particularly for relative newbies.
in a FRESHWATER tank? or am I reading this WRONG 
for them.
) and pimeloid species are particually affected by nitrates over 50 to 60 ppm, high nitrates cause their whiskers to whither away and if not reduced ultimately cause the death of the fish. Other fish that are affected are amazonian cichlids (discus and appisto's) and L number type plecos. Testing for nitrates is as much a part of the FW hobby as it is for the SW hobby although not needed as often (i only test about once every two weeks).
