Floating pointing incrementing, not working

Here is my code so far. Im pretty new to the language, any help would be great
Matt

#include <LiquidCrystal.h>
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12,11,10,9,8,7);




byte sensorInterrupt = 0;  // 0 = pin 2; 1 = pin 3
byte sensorPin       = 2;

// The hall-effect flow sensor outputs aproximatly one pulse per .00038L

volatile byte pulseCount;  

float flowRate;
unsigned int flowGallons;
float totalGallonsA;
unsigned int totalGallonsB;
int pulseCounttot;
unsigned long oldTime;

void setup()
{
 Serial.begin(9600);
 lcd.begin(16, 2);
 lcd.setCursor(0, 0);
 lcd.print("BRADSHAW ");
 lcd.setCursor(0, 1);
 lcd.print("INDUSTRIES ");

delay(3000);
 lcd.clear();





 pinMode(sensorPin, INPUT);
 digitalWrite(sensorPin, HIGH);

 pulseCount        = 0;
 flowRate          = 0.0;
 flowGallons       = 0;
 totalGallonsA     = 0;
 totalGallonsB     = 0;
 oldTime           = 0;
 pulseCounttot     = 0;
 // The Hall-effect sensor is connected to pin 2 which uses interrupt 0.
 // Configured to trigger on a FALLING state change (transition from HIGH
 // state to LOW state)
 attachInterrupt(sensorInterrupt, pulseCounter, FALLING);
}

/**
* Main program loop
*/
void loop()
{




 if((millis() - oldTime) >= 1000)    // Only process counters once per second
 { 
   // Disable the interrupt while calculating flow rate and sending the value to
   // the host
   detachInterrupt(sensorInterrupt);


   // Because this loop may not complete in exactly 1 second intervals we calculate
   // the number of milliseconds that have passed since the last execution and use
   // that to scale the output. 
 
       unsigned long time = millis() - oldTime;
      float time_in_sec = time / 1000;
      float impuls = pulseCount * time_in_sec; //scale pulse number


     float flowG = impuls * .00010;  // amount of gals
      float GPH = flowG * 120 ;  // convert to gph


      totalGallonsA =+ flowG ;


   oldTime = millis();
   {

   }
   lcd.setCursor(0,0);
   lcd.print(GPH);
   lcd.setCursor(6,0);
   lcd.print("GPH");   // Print the integer part of the variable
   lcd.setCursor(0,1);
   lcd.print(totalGallonsA,4);



   // Reset the pulse counter so we can start incrementing again
   pulseCount = 0;

   // Enable the interrupt again now that we've finished sending output
   attachInterrupt(sensorInterrupt, pulseCounter, FALLING);
 }
}

/**
* Invoked by interrupt0 once per rotation of the hall-effect sensor. Interrupt
* handlers should be kept as small as possible so they return quickly.
*/
void pulseCounter()
{
 // Increment the pulse counter
 pulseCount++;
}