Hard water combines with soap to form insoluble calcium or magnesium soap scum. Sodium carbonate softens water by precipitating calcium/magnesium as insoluble carbonates (removing them from solution) and converts soap scum back into soluble sodium soaps.
: While Soda Crystals are generally safe, avoid excessive use of highly corrosive "caustic soda" (sodium hydroxide) if you have uPVC pipes, as it can generate heat that warps them if it doesn't dissolve properly.
Using soda crystals to unblock a drain is a simple, cost-effective, and environmentally friendly method that can be quite effective for minor blockages. For more severe blockages or if you're unsure about the cause of the blockage, it might be best to consult a professional plumber.
The most common drain blockages are FOGs from cooking and personal care products. Soda crystals react with free fatty acids in these fats to form (sodium carboxylate salts) and glycerol. The reaction is: