I would use pure salt. "Aquarium salt" as sold by LFS is usually pure salt, though it does cost more simply because it is labelled as for use in aquariums.
Okay so I went today to grab some and they had tonic salt ,so I put 1 and a half tablespoons in my tank during a water change and tomorrow I will add the other half ,is it normal that my tank has gone quite cloudy and foggy ,I mean I did add some plant tablets for the plants and they kind of disintegrated.
If your bristlenose plecos start shaking and acting crazy then do a 25% water change to dilute the salt some. I usually do 1/2 doses with my plecos because they hate salt.