Index: firmware/App/Modes/ModeDrain.c
===================================================================
diff -u -re107dacab9f6c78574f1c26e1004e0dbdc8dba03 -r79d0c6ca5e03581ba1b4a142f5b450bf4547dded
--- firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision e107dacab9f6c78574f1c26e1004e0dbdc8dba03)
+++ firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 79d0c6ca5e03581ba1b4a142f5b450bf4547dded)
@@ -7,8 +7,8 @@
 *
 * @file    ModeDrain.c
 *
-* @author  (last)      Dara Navaei
-* @date    (last)      11-Jan-2023
+* @author  (last)      Bill Bracken
+* @date    (last)      17-Jan-2023
 *
 * @author  (original)  Leonardo Baloa
 * @date    (original)  20-Dec-2019
@@ -55,8 +55,21 @@
 #define RINSE_CONCENTRATE_LINES_WAIT             ( 25 * MS_PER_SECOND / TASK_GENERAL_INTERVAL )        ///< Time period to wait for concentrate lines to rinse.
 
 #define RINSE_SPEED                              ( ( CONCENTRATE_PUMP_MAX_SPEED - 3.0F ) * -1.0F )     ///< Reserver the concentrate speed to rinse out concentrate lines.
-#define CONCENTRATION_BOTTLE_LOW_VOLUME_ML       100.0F                                                ///< Concentration bottle low volume in mL.
 
+#define CONCENTRATE_BOTTLE_PRIMING_VOL_ML        73.0F                                                 ///< Concentrate bottle priming volume in mL.
+#define CONCENTRATE_BOTTLE_RESERVOIOR_VOL_ML     1500.0F                                               ///< Concentrate bottle reservoir volume in mL
+#define CONCENTRATE_BOTTLE_RESERVOIOR_FILLS      3                                                     ///< Concentrate bottle reservoir vlls.
+#define BICARB_PERCENT_FILL                      0.03514F                                              ///< Bicarb volume percentage of reservoir volume.
+#define ACID_PERCENT_FILL                        0.02222F                                              ///< Acid volume percentage of reservoir volume.
+
+///< Concentrate bottle acid low volume in mL.
+static const F32 CONCENTRATE_BOTTLE_ACID_LOW_VOLUME_ML   = ( CONCENTRATE_BOTTLE_PRIMING_VOL_ML +
+                                                             ( CONCENTRATE_BOTTLE_RESERVOIOR_VOL_ML * CONCENTRATE_BOTTLE_RESERVOIOR_FILLS * ACID_PERCENT_FILL) );
+
+///< Concentrate bottle bicarb low volume in mL.
+static const F32 CONCENTRATE_BOTTLE_BICARB_LOW_VOLUME_ML = ( CONCENTRATE_BOTTLE_PRIMING_VOL_ML +
+                                                             ( CONCENTRATE_BOTTLE_RESERVOIOR_VOL_ML * CONCENTRATE_BOTTLE_RESERVOIOR_FILLS * BICARB_PERCENT_FILL) );
+
 // ********** private data **********
 
 static DG_DRAIN_STATE_T drainState;                                                                    ///< Currently active drain state.
@@ -261,14 +274,14 @@
 #endif
         {
             // Detect empty bottles using integrated volumes
-            if ( ( acidBottleVolML - getChemicalUsedVolumeML( ACID ) ) <= CONCENTRATION_BOTTLE_LOW_VOLUME_ML ) // ||  // SRSDG 437
+            if ( ( acidBottleVolML - getChemicalUsedVolumeML( ACID ) ) <= CONCENTRATE_BOTTLE_ACID_LOW_VOLUME_ML ) // SRSDG 836
             {
                 resetChemicalUsedVolumeML( ACID );
                 setThisFisrtFillFlag( TRUE );                                 // indicates bottles need prime
                 activateAlarmNoData( ALARM_ID_DG_ACID_BOTTLE_LOW_VOLUME );
             }
 
-            if ( ( bicarbBottleVolML - getChemicalUsedVolumeML( BICARB ) ) <= CONCENTRATION_BOTTLE_LOW_VOLUME_ML )  // || // SRSDG 438
+            if ( ( bicarbBottleVolML - getChemicalUsedVolumeML( BICARB ) ) <= CONCENTRATE_BOTTLE_BICARB_LOW_VOLUME_ML )  // SRSDG 837
             {
                 resetChemicalUsedVolumeML( BICARB );
                 setThisFisrtFillFlag( TRUE );