Sodium carbonate (NaCO3) or Soda Crystals is a sodium salt of carbonic acid.
It is used as a water softener, that is it reduces the GH of water.
Care should be taken as the pH of the water will rise sharply if there is not sufficient buffering (KH) in the water to slow it and if it rises too quickly then species which are pH change intolerant may be greatly stressed or even die. A pH change of no more than 0.5 in 24 hours is recommended.
- Salt intolerant fish may not like the high levels of Sodium in the water.