determine the amounts of mineral acid required to achieve the object of the invention in any particular instance is well within the capability of the person skilled in the art as a generality however solutions containing at least about 30 of active phosphonic acid will usually be stable provided they contain more than 0 40 e g from about 0 41 to about 0 55 gram equivalents of non oxidizing mineral acid per 100 grams of solution in some instances the minimum concentration of mineral acid required for stability will be towards the upper end of this range moreover solutions containing about 50 or more of active phosphonic acid are in some instances stabilized by the presence of 0 40 gram equivalents of mineral acid or less provided they contain at least 10 preferably at least 12 of hcl in addition to the aforementioned amp acid and non oxidizing mineral acids the compositions claimed herein can include various other constituents which do not prevent substantial realization of advantages of this invention e g such other constituents may include other metal sequestrants e g other polymethylenephosphonic acids such as nitrilotri methylenephosphonic acid ethylenediaminetetra methylenephosphonic acid and triethylenetetraminehexa methylenephosphonic acid solutions 1 34 containing various concentrations of active phosphonic acid and hcl were prepared by additions of 32 hcl solution or 32 hcl solution and water to samples of a commercially available product which is an aqueous solution containing 6 86 hcl and 50 4 of active phosphonic acid corresponding.