Sodium carbonate, Na2CO3, (also known as washing soda, soda ash and soda crystals, and in the monohydrate form as crystal carbonate) is the water-soluble sodium salt of carbonic acid.
S 4035 (OTTO) Sodium carbonate, anhydrous, 99.999% Cas 497-19-8 - used in some aquarium water pH buffers to maintain a desired pH and carbonate hardness.