the present invention provides a substantially phosphate - free neutral ph , stable transition metal salt / polymer corrosion / deposition inhibition combination for treatment of aqueous systems . the combination of the present invention avoids the use of acidity or alkalinity to provide product stability . the stability of the combination of the present invention avoids the field application problems of prior transition metal salt - based treatment combinations . according to the present invention , a corrosion / deposition inhibiting combination for metal surfaces exposed to an aqueous system comprises ( i ) a water soluble divalent treatment metal salt , and a polymer component preferably ( ii ) a low molecular weight acrylate copolymer , and ( iii ) a poly ( ether carboxylate ) along with ( iv ) an aliphatic hydroxycarboxylic acid stabilizer . it was discovered that the inclusion of an aliphatic hydroxycarboxylic acid in the divalent transition metal salt / polymer mixture provided for stability at neutral ph while also enhancing corrosion inhibition . the water soluble divalent transition metal salt of the present invention can include any metal salt which provides a divalent ion upon disassociation in water . a preferred example are water soluble zinc salts which provide zn + 2 ions in aqueous solution . convenient sources of such salts includes zinc oxide , zinc chloride , and zinc sulfate . the preferred source of the zn + 2 ion is zinc sulfate . the polymer component of the present invention includes any conventional corrosion / deposition inhibiting polymer or copolymer . preferably , the polymer component is a combination of a poly ( ether carboxylate ) and a low molecular weight acrylate copolymer . the preferred poly ( ether carboxylate ) according to the present invention is preferably a polyepoxysuccinic acid of the general formula : ## str1 ## wherein n ranges from about 2 - 11 , m is hydrogen or a water soluble cation such as na + , nh 4 + , or k + and r is hydrogen , c 1 - 4 alkyl or c1 - 4 substituted alkyl . preferably r is hydrogen . the preferred low molecular weight acrylate copolymer according to the present invention is preferably a polymer characterized by the structural formula : ## str2 ## wherein r 1 is h or lower alkyl ( c 1 - c 3 ); r 2 is oh , om 1 or nh 2 ; m 1 is a water soluble cation ; r 3 is a hydroxy substituted alkyl or alkalene radical having from 1 to 6 carbon atoms or a non - substituted alkyl or alkalene radical having from 1 to about 6 carbon atoms ; x , when present is an 5 anionic radical selected from the group consisting of so 3 , po 3 , po 4 and coo ; z , when present is hydrogen or any water soluble cation or cations which together counterbalance the valence of the anionic radical ; a is 0 or 1 . the number average molecular weight of the water soluble copolymer of formula ii may fall within the range of about 1 , 000 to about 500 , 000 with the range of about 1 , 500 to about 10 , 000 being preferred . the molar ratio x : y of the monomer of formula ii may fall within the range of about 30 : 1 to about 1 : 20 with the x : y molar ratio range from about 10 : 1 to about 1 : 5 being preferred . a preferred polymer is : ## str3 ## wherein m &# 39 ; is the same as given in formula ii above . this polymer ( formula iii ) is referred to as acrylic acid / allyl hydroxy propyl sulfonate ether ( aa / ahpse ). the iupac nomenclature for ahpse is 1 - propane sulfonic acid , 2 - hydroxy - 3 -( 2 - propenyl oxy )- mono sodium salt . the aliphatic hydroxy carboxylic acid according to the present invention pr eferably has a carbon n umber of 7 or less . the material may be selected from the group gluconic acid , succinic acid , citric acid , maleic acid , glutaric acid , adipic acid , and mixtures thereof . preferably the alphatic hydroxy carboxylic acid is citric acid . the combination of a water soluble divalent transition metal salt , a low molecular weight acrylic copolymer , a poly ( ether carboxylate ), and an aliphatic hydroxy carboxylic acid of the present invention is adjusted to a neutral ph by the addition of an alkalyzing agent such as koh . a neutral ph , stable combination of the present invention may be used in combination with other water treatment agents including corrosion inhibitors , conventional scale and contamination inhibitors , metal ion sequestering agents , biocides and other conventional water treatment agents . generally , the corrosion / deposition inhibiting combination of the present invention is added to an aqueous system to be treated at concentrations ranging from about 5 ppm to about 500 ppm as product preferably the treatment concentration of the combination of the present invention ranges from 5 ppm to about 200 ppm . typical treatment concentrations for the individual preferred components of the combination of the present invention are as follows : from about 0 . 2 to 10 parts per million water soluble divalent transition metal salt ; from about 2 to about 20 parts per million low molecular weight acrylic copolymers ; from about 2 to about 20 parts per million poly ( ether carboxylate ); and from about 0 . 5 to about 20 parts per million aliphatic hydroxy carboxylic acid . the ratio of the aliphatic hydroxy carboxylic acid to the divalent metal salt is preferably about 2 : 1 . the ratio of the water soluble acrylate copolymer to the divalent transition metal salt ( on an active basis ) preferably ranges from about 3 : 1 to about 6 : 1 . the poly ( ether carboxylate ) is used in a polymer to active divalent metal in a ratio in a range from about 3 : 1 to about 8 : 1 . the present invention will now be further described with reference to a number of specific examples which are to be regarded solely as illustrative , and not as restricting the scope of the present invention . testing was undertaken in a laboratory scale recirculating heat transfer apparatus . the corrosion inhibiting activity of a treatment comprising 6 parts per million polyexpoxysuccinic acid , 8 parts per million acrylic acid / allyl hydroxy propyl sulfonate ether ; 1 . 5 parts per million as zinc sulfate monohydrate when applied at a 100 parts per million dosage both with and without about 5 % citric acid . these treatment combinations were added to a recirculating cooling water containing 400 parts per million ca , 150 parts per million mg , 210 parts per million m - alkalinity ( as caco 3 ), 2 parts per million orthophosphate and 51 parts per million sio 2 at ph 8 . 6 in a specific conductance of about 2 , 200 microohms . the metallurgy tested included low carbon steel ( lcs ) coupons and an lcs heat transfer probe which generated a heat flux of 8 , 000 btu / square feet per hour . the bulk water temperature was 120 ° f ., and water velocity was at 2 . 8 feet per second . retention time was 1 . 4 days . table 1 summarizes the test results . table 1______________________________________ lcs appearance lcs coupon pitting heat transfer pittingproduct ( mpy ) density depth density depth______________________________________without citric 0 . 5 1 × 10 . sup . 4 / m . sup . 2 n / a 1 × 10 . sup . 4 / m . sup . 2 26 micronacidwith citric acid 0 . 2 clean n / a clean n / a______________________________________ the data in table 1 shows that the addition of an aliphatic hydroxycarboxylic acid to the treatment combination enhanced the overall corrosion inhibition as well as decreasing the pitting corrosion . the aliphatic hydroxycarboxylic acid also allows adjustment to neutral ph with no adverse impact on product stability . while this invention has been described with respect to particular embodiments thereof , it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art . the appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention .