I am confused on your salt ratio recomendations, and on the tilapia not being able to tolerate anything higher. My tilapia, now in for the winter are in considerably higher concentrations with apparantly no ill effects. Also both the Univ. of HI, and the UVI are currently conducting studies on, and breeding programs for tilapia in brackish and sea water. I am sure I the PDF on that around here if you want it. I just have to find it.