In very alkaline water ( pH ) 10.4 ) , the predominant ( ) 50 % ) form is carbonate .
In neutral or slightly alkaline water ( pH ) 6.5 ) , the bicarbonate form predominates ( ) 50 % ) becoming the most prevalent ( ) 95 % ) at the pH of seawater , while in very alkaline water ( pH ) 10.4 ) the predominant ( ) 50 % ) form is carbonate .