Conceptual Models > Equilibrium assumptions

Calculated Total Alkalinity in brine completely different than measured

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Idoboro:
Hello there,

I work with reverse osmosis desalination brines originate from the Mediterranean sea and I tried to model my solution with PHREEQC and gave it its chemical composition (pH, Na, K, Mg, Ca, Cl, SO4 and DIC). The solution input and description are attached in the end. Due to the high ionic strength of my solution, I work with Pitzer database.

In the output PHREEQC calculated the water Total Alkalinity to be ~0.57 meq/kg which is much lower than the Alkalinity that I measured which was ~4.7 meq/kg and also much lower than regular seawater alkalinity.

Does anybody know where this huge error can come from and how can it be dealt with?
Is it okay that I inserted the DIC value that I measured as C?

I'll appreciate any help.

EQUILIBRIUM_PHASES 1 Equilibrium with atmosphere
       CO2(g)    -3.376 10
       O2(g)     -0.6778 10
   SOLUTION 1 Sorek Brine-PITZER
       temp      25
       pH        8.125
       pe        4
       redox     pe
       units     mmol/l
       density   1.05
       C         4305 uMol/l
       Ca        23
       Cl        1170
       K         44
       Mg        116
       Na        1004
       S         65
       water    1 # kg
------------------------Description of solution----------------------------

                                       pH  =   8.125   
                                       pe  =   4.000   
                        Activity of water  =   0.959
                 Ionic strength (mol/kgw)  =   1.547e+00
                       Mass of water (kg)  =   1.000e+00
                 Total alkalinity (eq/kg)  =   5.676e-04
                       Total CO2 (mol/kg)  =   4.403e-03
                         Temperature (?C)  =  25.00
                  Electrical balance (eq)  =   2.162e-02
 Percent error, 100*(Cat-|An|)/(Cat+|An|)  =   0.81
                               Iterations  =  17
                         Gamma iterations  =   4
                      Osmotic coefficient  =   0.93438
                                  Total H  = 1.110207e+02
                                  Total O  = 5.578753e+01

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