Before jumping to conclusions about neons dying as a result of salt, let me try and explain how salt affects the fish ( a bit lengthy)
Depending on the natural habitats of the fish they are accustomed to living in salty, brackish or freshwater. Hence their bodies have learned over the years to maintain an Osmotic balance between their bodies and their environment.
In the case of fish living in salty water the salt levels in their body are lower than the water which causes the salts from the water to permeate into their bodies. Therefore these fish need to get rid of excess salts through their urine at regular intervals in concentrated form.
In the case of fish living in fresh water the salt levels in their body are higher than the water which causes the water to permeate into their bodies. Therefore these fish need to get rid of excess water through their urine at regular intervals whilst retaining the salts.
Therefore the theory goes that if the salt content in the water matches their internal salts then the fish is subject to less Osmotic stress and can therfore use its energy to combat diseases etc. Hence the reason why a lot of fish keepers recommend use of salt for curative purposes.
Also we need to consider the fact that in the fishkeepers world, fish have become accustomed to the LFS environment rather than their natural habitat. Therefore their ability to adjust to salt contents is also very different.
I hope this clarifies the salt issue.
