Alkylene phosphonic acid scale inhibitor compositions

An improved organic phosphonic acid threshold agent for inhibiting scale formation by alkaline earth metal salts which comprises a piperazine phosphonic acid derivative having the formula ##STR13## wherein R is hydrogen, hydroxyethyl, hydroxypropyl, methylenesulfonate, hydroxyethylsulfonate, hydroxypropylsulfonate, carboxymethyl or ##STR14## and wherein M is hydrogen, an alkali metal, an ammonium or a di- or triethanolamine radical in combination with a phosphonic acid derivative of an amine having the formula ##STR15## wherein n is 0-14 and wherein M has the aforesaid meaning;

• or an organic phosphonate derivative having the formula ##STR16## wherein R is an alkyl radical having 1-3 carbon atoms and M has the aforesaid meaning;
• or a polymer having the formula A(BA).sub.m wherein A is an organic radical having the formula ##STR17## wherein Z is hydrogen, hydroxyethyl, hydroxypropyl, ##STR18## or BA and M is a H, Na or NH.sub.4 radical and wherein at least 50% of the Z groups are ##STR19## B is a moiety derived from ethylene dichloride or epichlorohydrin and m is 1 or 2, with the proviso that at least 50% of the R groups of the (a) component are ##STR20## wherein the (a) component comprises from about 50 to 95% of the combination threshold agent.