diff --git a/src/sas/qtgui/Calculators/SldPanel.py b/src/sas/qtgui/Calculators/SldPanel.py
index 54fc5c0917..5ddf6ad931 100644
--- a/src/sas/qtgui/Calculators/SldPanel.py
+++ b/src/sas/qtgui/Calculators/SldPanel.py
@@ -116,11 +116,8 @@ def setupUi(self):
         self.ui.setupUi(self)
 
         # set validators
-        # TODO: GuiUtils.FormulaValidator() crashes with Qt5 - fix
-        #self.ui.editMolecularFormula.setValidator(GuiUtils.FormulaValidator(self.ui.editMolecularFormula))
-
-        # No need for recalculate
-        self.ui.recalculateButton.setVisible(False)
+        # Chemical formula is checked via periodictable.formula module.
+        self.ui.editMolecularFormula.setValidator(GuiUtils.FormulaValidator(self.ui.editMolecularFormula))
 
         rx = QtCore.QRegularExpression("[+\-]?(?:0|[1-9]\d*)(?:\.\d*)?(?:[eE][+\-]?\d+)?")
         self.ui.editMassDensity.setValidator(QtGui.QRegularExpressionValidator(rx, self.ui.editMassDensity))
@@ -130,7 +127,7 @@ def setupUi(self):
         # signals
         self.ui.helpButton.clicked.connect(self.displayHelp)
         self.ui.closeButton.clicked.connect(self.closePanel)
-        self.ui.recalculateButton.clicked.connect(self.calculateSLD)
+        self.ui.calculateButton.clicked.connect(self.calculateSLD)
 
     def calculateSLD(self):
         self.recalculateSLD()
@@ -147,11 +144,6 @@ def setupModel(self):
 
         #self.model.dataChanged.connect(self.dataChanged)
 
-        self.ui.editMassDensity.textChanged.connect(self.recalculateSLD)
-        self.ui.editMolecularFormula.textChanged.connect(self.recalculateSLD)
-        self.ui.editNeutronWavelength.textChanged.connect(self.recalculateSLD)
-        self.ui.editXrayWavelength.textChanged.connect(self.recalculateSLD)
-
         self.modelReset()
 
     def setupMapper(self):
diff --git a/src/sas/qtgui/Calculators/UI/SldPanel.ui b/src/sas/qtgui/Calculators/UI/SldPanel.ui
index 82838a9617..df0197accc 100644
--- a/src/sas/qtgui/Calculators/UI/SldPanel.ui
+++ b/src/sas/qtgui/Calculators/UI/SldPanel.ui
@@ -322,7 +322,7 @@
      </property>
      <layout class="QGridLayout" name="gridLayout">
       <item row="0" column="0">
-       <widget class="QPushButton" name="recalculateButton">
+       <widget class="QPushButton" name="calculateButton">
         <property name="enabled">
          <bool>true</bool>
         </property>
@@ -336,7 +336,10 @@
          <enum>Qt::NoFocus</enum>
         </property>
         <property name="text">
-         <string>Recalculate</string>
+         <string>Calculate</string>
+        </property>
+        <property name="autoDefault">
+         <bool>true</bool>
         </property>
        </widget>
       </item>
@@ -364,6 +367,9 @@
         <property name="text">
          <string>Close</string>
         </property>
+        <property name="autoDefault">
+         <bool>false</bool>
+        </property>
        </widget>
       </item>
       <item row="0" column="3">
@@ -377,6 +383,9 @@
         <property name="text">
          <string>Help</string>
         </property>
+        <property name="autoDefault">
+         <bool>false</bool>
+        </property>
        </widget>
       </item>
      </layout>
@@ -398,7 +407,7 @@
   <tabstop>editNeutronLength</tabstop>
   <tabstop>closeButton</tabstop>
   <tabstop>helpButton</tabstop>
-  <tabstop>recalculateButton</tabstop>
+  <tabstop>calculateButton</tabstop>
  </tabstops>
  <resources/>
  <connections/>
diff --git a/src/sas/qtgui/Utilities/GuiUtils.py b/src/sas/qtgui/Utilities/GuiUtils.py
index b04db50d16..6898c11a0a 100644
--- a/src/sas/qtgui/Utilities/GuiUtils.py
+++ b/src/sas/qtgui/Utilities/GuiUtils.py
@@ -741,16 +741,15 @@ def __init__(self, parent=None):
     def validate(self, input, pos):
 
         self._setStyleSheet("")
-        return QtGui.QValidator.Acceptable, pos
 
-        #try:
-        #    Formula(str(input))
-        #    self._setStyleSheet("")
-        #    return QtGui.QValidator.Acceptable, pos
+        try:
+            Formula(str(input))
+            self._setStyleSheet("")
+            return QtGui.QValidator.Acceptable
 
-        #except Exception as e:
-        #    self._setStyleSheet("background-color:pink;")
-        #    return QtGui.QValidator.Intermediate, pos
+        except Exception as e:
+            self._setStyleSheet("background-color:pink;")
+            return QtGui.QValidator.Intermediate
 
     def _setStyleSheet(self, value):
         try: