temperature controlled relay for a motor

Folks,

Newbie here. We have a pump that circulates water around a lake dock in the winter to help prevent it from freezing. When no one is there the motor runs constantly, even on nicer days when the temperature is well above freezing. Rather than having it run constantly, I thought a Nano, DHT22, and a SSR could help solve the problem.

I've got the circuit pretty much mapped out but it's the code that's giving me trouble. I'd like to use hysteresis (I didn’t know the word until two days ago), but I've never coded it before, plus I'm very new to programming anyway. Essentially, from what I understand, with hysteresis you look at the previous state of something. In this case, a motor, I guess. From what I understand, when the temperature reaches the low threshold, say 35 degrees, the pump comes on. It runs until the temperature reaches the upper threshold, say 45 degrees when the motor shuts off. Problem is I just can’t see the code. I’m just wasting paper here as I try to work in out by hand. Any help would be appreciated.

In the code below, the redLed takes place of the motor.  The greenLed is just a status light that should illuminate when the temp is above the upper threshold.  

Best,

Tony

#include "DHT_U.h"
#define Type DHT11

int sensePin=7;
DHT DHTT(sensePin, Type);

float humidity;
float tempC;
float tempF;

float lowerThresholdTemp = 35;
float upperThresholdTemp = 45;

int redLed = 9;
int greenLed = 11;
int lastMotorState = 0;

void setup() {
Serial.begin(9600);
DHTT.begin();
pinMode(redLed, OUTPUT);
pinMode(greenLed, OUTPUT);
}


void loop()
{
  humidity = DHTT.readHumidity();
  tempC = DHTT.readTemperature();
  tempF = DHTT.readTemperature(true);
  
  if (tempF < lowerThresholdTemp && lastMotorState==0)
  {
    digitalWrite(greenLed, LOW);
    digitalWrite(redLed, HIGH);
    lastMotorState = 1;
  }
  
  if (tempF >= upperThresholdTemp && lastMotorState==1)
  {
    digitalWrite(redLed, LOW);
    digitalWrite(greenLed, HIGH);
    lastmotorState = 0;
  }
  
  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.print(".   TempC: ");
  Serial.print(tempC);
  Serial.print(".   TempF: ");
  Serial.print(tempF);
  Serial.println(". ");

}