Magnesium oxide is an effective pH buffer for aqueous systems. At low dosages it may be used to extend polymer stability at high temperatures.
Soda Ash is used primarily to treat calcium contamination in water based muds and or make up water.
Sodium Bicarbonate is used in water base muds as a source of bicarbonate ions to precipitate calcium. It will reduce pH and is primarily used for treating cement contamination. Sodium Bicarbonate is soluble in water.