If salinity in excess of 6 parts per thousand kills them, I wonder if
they could be controlled by seeding the beds with rock salt??
Theoretically the large, heavy rock salt crystals should sink
quickly, with minimal dissolving on the way down; then dissolve on
the bottom, creating a dense bottom layer with salinity well over 6
parts per thousand; then gradually diffuse into the overlying water,
causing negligible increase in salinity to the main water mass??
What do you think?
 
Paul M.