High concentration of PO4 and zero DO concentration

I've modeled river-reservoir system. 5 tributaries are entered to river and the reservoir contains three branches. In Water quality simulation model, All inflow concentration of PO4 is correct. I've checked in "snp.opt" file but when the mathematical calculations have been done, the "Spatially integrated mass " of PO4 is about "0.41169542E+17 g" which is very large compared with previous period abou "0.41169542E+6 g ". The mass error value is in "E+6 g" scale. Furthermore the DO concentration become zero. It should be noticed that there is less changes in inflow and concentration. What should I do to fix the problem? I've presented the mass balance results in missing day in below.
Regards

Inflows
Upstream inflows
Branch 1
Layer [KQIN] = 31-31
Inflow [QIN] = 0.24 m^3/sec
Temperature [TIN] = 9.75 øC

Tributaries
Segment [ITR] = 7 17 19 25 33 44 61 56
Layer [KTWB] = 31-42 31-42 31-42 31-42 31-42 9-42 9-42 9-42
Inflow [QTR] = 0.57 0.10 0.72 4.34 0.45 81.92 0.32 0.31
Temperature [TTR] = 9.75 9.75 9.75 9.75 9.75 3.54 0.74 3.98

Outflows
Withdrawals
Segment [IWD] = 19
Outflow (m^3/sec) [QWD] = 2.23
Layer [KWD] = 31 32 33 34 35 36 37 38 39 40 41 42

Outflow (m^3/sec) [QSW] = 1.74 0.09 0.08 0.07 0.07 0.06 0.04 0.03 0.02 0.02 0.01 0.00

Withdrawals
Segment [IWD] = 33
Outflow (m^3/sec) [QWD] = 0.00
Layer [KWD] =
Outflow (m^3/sec) [QSW] = 0.00
Withdrawals
Segment [IWD] = 51
Outflow (m^3/sec) [QWD] = 0.00
Layer [KWD] =
Outflow (m^3/sec) [QSW] = 0.00
Withdrawals
Segment [IWD] = 41
Outflow (m^3/sec) [QWD] = 81.92
Layer [KWD] = 31 32 33 34 35 36 37 38 39 40 41 42

Outflow (m^3/sec) [QSW] = 18.68 7.03 6.79 6.74 6.53 6.46 6.20 6.12 5.89 5.84 2.84 2.81

Withdrawals
Segment [IWD] = 49
Outflow (m^3/sec) [QWD] = 0.32
Layer [KWD] = 9 10 11 12
Outflow (m^3/sec) [QSW] = 0.19 0.07 0.05 0.02
Withdrawals
Segment [IWD] = 51
Outflow (m^3/sec) [QWD] = 0.31
Layer [KWD] = 31 32 33 34 35 36 37 38 39 40 41 42

Outflow (m^3/sec) [QSW] = 0.00 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03

1Constituent Inflow Concentrations
Branch 1 [CIN]
Phosphate = 0.040 g/m^3
Nitrate-Nitrite = 5.000 g/m^3
Total iron = 5.000 g/m^3
CBOD = 10.000 g/m^3
Dissolved oxygen = 7.000 g/m^3
Tributary 1 [CTR]
Phosphate = 0.100 g/m^3
Nitrate-Nitrite = 5.000 g/m^3
Total iron = 0.201 g/m^3
CBOD = 10.000 g/m^3
Dissolved oxygen = 7.000 g/m^3
Tributary 2 [CTR]
Phosphate = 0.040 g/m^3
Nitrate-Nitrite = 5.000 g/m^3
Total iron = 0.117 g/m^3
CBOD = 10.000 g/m^3
Dissolved oxygen = 7.000 g/m^3
Tributary 3 [CTR]
Phosphate = 0.100 g/m^3
Nitrate-Nitrite = 1.780 g/m^3
Total iron = 0.071 g/m^3
CBOD = 10.000 g/m^3
Dissolved oxygen = 7.000 g/m^3
Tributary 4 [CTR]
Phosphate = 0.030 g/m^3
Nitrate-Nitrite = 3.840 g/m^3
Total iron = 0.500 g/m^3
CBOD = 10.000 g/m^3
Dissolved oxygen = 7.000 g/m^3
Tributary 5 [CTR]
Phosphate = 0.080 g/m^3
Nitrate-Nitrite = 5.000 g/m^3
Total iron = 0.212 g/m^3
CBOD = 10.000 g/m^3
Dissolved oxygen = 7.000 g/m^3

Water Balance
Waterbody 1
Spatial change [VOLSR] = 0.54079966E+07 m^3
Temporal change [VOLTR] = 0.54079966E+07 m^3
Volume error = 0.13257656E-03 m^3
Percent error = 0.24514912E-08 %
Branch 1
Spatial change [VOLSBR] = 0.54079966E+07 m^3
Temporal change [VOLTBR] = 0.54079966E+07 m^3
Volume error = 0.13257656E-03 m^3
Percent error = 0.24514912E-08 %

Energy Balance
Waterbody 1
Spatially integrated energy [ESR] = 0.16928760E+12 kJ
Temporally integrated energy [ETR] = 0.16928760E+12 kJ
Energy error = 0.41433558E+03 kJ
Percent error = 0.24475247E-06 %
Branch 1
Spatially integrated energy [ESBR] = 0.16928760E+12 kJ
Temporally integrated energy [ETBR] = 0.16929974E+12 kJ
Energy error = 0.41436529E+03 kJ
Percent error = 0.24475247E-06 %

Mass Balance
Branch 1
Phosphate
Spatially integrated mass [CMBRS] = 0.41169542E+17 g
Temporally integrated mass [CMBRT] = 0.41169542E+17 g
Mass error = -0.94020240E+07 g
Percent error = -0.22837329E-07 %
Nitrate-Nitrite
Spatially integrated mass [CMBRS] = 0.13296102E+08 g
Temporally integrated mass [CMBRT] = 0.13296102E+08 g
Mass error = -0.24959650E-02 g
Percent error = -0.18772156E-07 %
Total iron
Spatially integrated mass [CMBRS] = 0.38657540E+07 g
Temporally integrated mass [CMBRT] = 0.38657540E+07 g
Mass error = -0.77605434E-03 g
Percent error = -0.20075109E-07 %
CBOD
Spatially integrated mass [CMBRS] = -0.28161897E+19 g
Temporally integrated mass [CMBRT] = -0.28161897E+19 g
Mass error = 0.35596134E+09 g
Percent error = -0.12639821E-07 %
Algae
Spatially integrated mass [CMBRS] = 0.00000000E+00 g
Temporally integrated mass [CMBRT] = 0.00000000E+00 g
Mass error = 0.00000000E+00 g
Percent error = -0.12639821E-07 %
Dissolved oxygen
Spatially integrated mass [CMBRS] = -0.51931015E+19 g
Temporally integrated mass [CMBRT] = -0.51931015E+19 g
Mass error = 0.67753267E+09 g
Percent error = -0.13046783E-07 %