Methods are given for making scale inhibitors, that were previously incompatible with fluids containing fluoride ion, compatible with fluids containing fluoride ion. Examples of such scale inhibitors include phosphonates and phosphino-polycarboxylates. The method is replacing alkali metal and alkaline earth metal cations, present in salts or bases, or as counter ions of the scale inhibitors, with hydrogen or ammonium ions. Methods of inhibiting scale formation and of dissolving scales are also given.