Salt Therapy Air Purifier Refill - Salin Plus Filter Refill. Salin Plus uses a unique method in an advanced process for treating air. Air is forced through the filter which contains a micro-crystallized deposit of salts, primarily sodium chloride (98% NaCl, 0.5% calcium chloride and magnesium, 0.2% iodine and sulphur).. Salin Air Purifying Salt Therapy is believed to be of great benefits to people with respiratory conditions.