During winter, 0.05%, but dont add rock salt directly to the pond when the water is
cold and the salt may sink to the bottom and sit there undissolved and the fish
settle down onto it.
In summer up to 0.1% which wont affect plants. This is around 0.9lbs per 100
gallons.
For parasites there are medications that are known to work better than running salt
up to 0.3% . This concentration kills plants and (??? kills algae and biomedia???) I
dont know, but I would worry about that too. It also can stress the fish out and
trash fins.
The internal salt level of fish and humans is 0.9% ..
Ingrid