ive have a 1.5'' gsp i bought at walmart 2 years ago with two 6'' jaguar cichlids and ive added a little bit of doc wells aquaium salt and hes been doing just fine, my jags are scared of him. so far i havent noticed any problems with my gsp and the water salinity issue.
id seperate the GSP from the jags. they could both cause substantial damage to each other. but id pm pufferpunk about any Qs as i was a beginner then and now no longer have mine