Kribs are found in brackish enviroments in the wild so provided you increased the SG of the water slowly they could tolerate a SG of up to 1.005, chromides should also be fine with this although this would be the least ammount of salt they could live with.
If you are keeping a brackish tank you will need to purchase a hydrometer to measure the SG, teaspoons per gallon just isnt accurate enough but it works out at roughly 4 teaspoons of salt per gallon of water.