Epsom salt effect on PH

[Cactuspixie]

Are there fishes that cannot be treated with epsom salt because of its effect on ph?
In particular, I was wondering if fish in a soft acidic environment would be stressed and perhaps even killed by the increase in ph and hardness caused by this 'cure'.
I don't have a problem requiring the use of Epsom salts (yet) but I think it's a good idea to learn these things at ones leisure rather than wait till there is sickness and one is in a blind panic

 

[HUKIT]

Epsom salt will have little to no effect on pH but raises general hardness.

 

[Cactuspixie]

Epsom salt will have little to no effect on pH but raises general hardness.

Thanks for your reply Hukit!
I thought an increase in hardness would itself cause the ph to rise.
So it would be a safe treatment for a blackwater biotope?