When I received some baby bristlenose with very persistent ich I had to use 5 tablespoons of salt in 10 gallons and while they may not have been happy I would think if they were very sensitive it would have wiped them out. That's a lot of salt.
The commonly available BN is a tough fish. I would say one of the biggest risk factors is not enough veggie matter/fiber for the amount of protein they are eating. Swamp wood, coconuts with coir still on them and veggies to graze on seem to help a lot. Mine demolish zucchinis like there is no tomorrow.