Which salt is preferable?

We suggest using rock salt/sendha namak in place or ordinary white table salt.  This is a natural salt - not gone through refinement, or chemicalisation. Himalayan pink salt is also one type of rock salt. 

On the other hand, avoid having white salt. White salt is bleached many times. Salt in its natural form is not white. Table salt is usually coloured with bleaching agents so as to make it white.