Index: firmware/App/Modes/ModeFill.c
===================================================================
diff -u -r81769c6bea6ed32d70698fb03ad5823de1814b27 -re95b1d3c47166be8a6852818a70b4c6231881b86
--- firmware/App/Modes/ModeFill.c	(.../ModeFill.c)	(revision 81769c6bea6ed32d70698fb03ad5823de1814b27)
+++ firmware/App/Modes/ModeFill.c	(.../ModeFill.c)	(revision e95b1d3c47166be8a6852818a70b4c6231881b86)
@@ -74,6 +74,9 @@
 #define CONCENTRATE_TEST_TIME_OUT_MS                    ( 30 * MS_PER_SECOND )                               ///< Concentrate test time out period in ms.
 #define DELAY_FMP_CHECK_START_BY_MS                     ( 10 * MS_PER_SECOND )                               ///< Delay start of FMP check during dialysate deliver state by this amount of time (in ms).
 
+#define MAX_RO_REJECTION_RATIO_ALLOW                    0.10F                                                ///< Maximum RO rejection ratio.
+#define MAX_CPO_CONDUCTIVITY_ALLOW                      100.0F                                               ///< Maximum CPo sensor conductivity value.
+
 // 2m long tubing to cap = 19.5 mL (acid line) + 7.92 mL/m * 2 m (tubing to cap) + 20.82 mL (straw) = 56.15 mL
 // Prime time in seconds = ( 56.15 mL / 48 mL/min ) x 60 second/min + 25 seconds margin time = 95 seconds.
 #define PRIME_CONCENTRATE_LINES_TIME_OUT_MS             ( 95 * MS_PER_SECOND )                               ///< Time required to prime the concentrate lines.
@@ -129,6 +132,10 @@
 static F32 totalBicarbConductivity;                                                                          ///< Total bicarb conductivity over 30 seconds.
 static F32 totalAcidConductivity;                                                                            ///< Total acid conductivity over 30 seconds.
 
+static F32 sumFillCPoConductivity;                                                                           ///< Sum of CPo conductivity readings over course of a fill to calculate an average at end of fill.
+static F32 sumFillRejRatio;                                                                                  ///< Sum of Rejection Ratio values over course of a fill to calculate an average at end of fill.
+static U32 fillCPoConductivitySampleCnt;                                                                     ///< Number of samples in sum of CPo and Rej. Ratio conductivity readings for fill.
+
 static U32 pumpSpeedIndex;                                                                                   ///< Index used to access the desired pump speed in roPumpFlushBubblesSpeed table.
 static BOOL havePauseActuatorsBeenSet;                                                                       ///< Flag to indicate the actuators have been set to pause for the first time.
 static OVERRIDE_F32_T usedAcidVolumeML = { 0.0, 0.0, 0.0, 0.0 };                                             ///< The integrated acid concentration volume has been used in mL.
@@ -186,6 +193,9 @@
     totalBicarbConductivity       = 0.0F;
     totalAcidConductivity         = 0.0F;
     havePauseActuatorsBeenSet     = FALSE;
+    sumFillCPoConductivity        = 0.0F;
+    sumFillRejRatio               = 0.0F;
+    fillCPoConductivitySampleCnt  = 0;
 }
 
 /*********************************************************************//**
@@ -226,7 +236,6 @@
  *************************************************************************/
 U32 execFillMode( void )
 {
-    checkRORejectionRatio();
     checkDialysateTemperatureSensors();
     setHeaterTargetTemperature( DG_PRIMARY_HEATER, getPrimaryHeaterTargetTemperature() );
 
@@ -722,10 +731,10 @@
     {
         setValveState( VPO, VALVE_STATE_FILL_C_TO_NC );
 
-        dialysateFillStartTime     = getMSTimerCount();
+        dialysateFillStartTime        = getMSTimerCount();
 
-        fillStatus.isThisFirstFill = FALSE;
-        result                     = DG_FILL_MODE_STATE_DELIVER_DIALYSATE;
+        fillStatus.isThisFirstFill    = FALSE;
+        result                        = DG_FILL_MODE_STATE_DELIVER_DIALYSATE;
     }
 
     return result;
@@ -750,6 +759,9 @@
     F32 acidConductivity            = getConductivityValue( CONDUCTIVITYSENSORS_CD1_SENSOR );
     F32 bicarbConductivity          = getConductivityValue( CONDUCTIVITYSENSORS_CD2_SENSOR );
     F32 inletTemperature            = getTemperatureValue( (U32)TEMPSENSORS_CONDUCTIVITY_SENSOR_2 );
+    F32 cpi                         = getConductivityValue( CONDUCTIVITYSENSORS_CPI_SENSOR );
+    F32 cpo                         = getConductivityValue( CONDUCTIVITYSENSORS_CPO_SENSOR );
+    F32 rejRatio                    = RO_REJECTION_RATIO_OUT_OF_RANGE_VALUE;  // default 1:1 before calculation in case can't divide by zero.
 
 #ifndef _RELEASE_
     if ( ( HW_CONFIG_BETA == getHardwareConfigStatus() ) ||
@@ -768,6 +780,15 @@
     // Set concentrate pumps speed based on the RO pump flow rate
     handleDialysateMixing( getMeasuredFlowRateLPM( RO_FLOW_SENSOR ) * ML_PER_LITER, acidMix, bicarbMix );
 
+    // Sum conductivity readings for CPo and RR checks
+    if ( fabs(cpi) >= NEARLY_ZERO )
+    {
+        rejRatio = cpo / cpi;
+    }
+    sumFillCPoConductivity      += cpo;
+    sumFillRejRatio             += rejRatio;
+    fillCPoConductivitySampleCnt++;
+
     // Delay start of FMP check, then begin integrating flow to a volume
     if ( TRUE == didTimeout( dialysateFillStartTime, DELAY_FMP_CHECK_START_BY_MS ) )
     {
@@ -808,7 +829,28 @@
         F32 acidNormalConductivity                   = acid.acidConcentrate[ CAL_DATA_ACID_CONCENTRATE_1 ].acidConductivityUSPerCM;
         F32 bicarbNormalConductivity                 = bicarb.bicarbConcentrate[ CAL_DATA_BICARB_CONCENTRATE_1 ].bicarbConductivityUSPerCM;
 
+        // Check RO filter
 #ifndef _RELEASE_
+        if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_RO_RATIO_CHECK ) != SW_CONFIG_ENABLE_VALUE )
+#endif
+        {
+            F32 avgCPo = sumFillCPoConductivity / (F32)fillCPoConductivitySampleCnt;  // sample count incremented above w/o condition so no need for divide by zero checks
+            F32 avgRR  = sumFillRejRatio / (F32)fillCPoConductivitySampleCnt;
+
+            if ( avgCPo > MAX_CPO_CONDUCTIVITY_ALLOW )
+            {
+                // Fault alarm per PRS 483
+                SET_ALARM_WITH_2_F32_DATA( ALARM_ID_DG_OUTLET_PRIMARY_CONDUCTIVITY_OUT_OF_RANGE, avgCPo, MAX_CPO_CONDUCTIVITY_ALLOW );
+            }
+            if ( avgRR > MAX_RO_REJECTION_RATIO_ALLOW )
+            {
+                // Fault alarm per PRS 483
+                SET_ALARM_WITH_2_F32_DATA( ALARM_ID_RO_REJECTION_RATIO_OUT_OF_RANGE, avgRR, MAX_RO_REJECTION_RATIO_ALLOW );
+            }
+        }
+
+        // Check FMP vs. LC
+#ifndef _RELEASE_
         if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_FLOW_VS_LOAD_CELL_CHECK_IN_FILL ) != SW_CONFIG_ENABLE_VALUE )
 #endif
         {
@@ -818,6 +860,7 @@
             }
         }
 
+        // Check mixing via avg. conductivities
 #ifndef _RELEASE_
         if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_MIXING_IN_FILL ) != SW_CONFIG_ENABLE_VALUE )
 #endif