Thanks Steve,
I did read between "ground and pin" this time and understood that the readings vary on tank capacity and distance between probes. In my test setup I am using the "actual probe" in a small and long PVC container where I manage submerge all 4 probes and below are the readings of my 10 different attempts.
1st Probe - 400-450
2nd Probe- 400-450
3rd Probe- 450-500
4th Probe- 600- 700
I had test the same is a glass of water with a small setup of probes and it show completely different readings.
I also found that readings fluctuate a bit and then stabilize itself in 5-10 seconds when I move from battery power to wall socket power and vice versa while reading values in my laptop, but this should be fine.
For now I have choose to read anything below 800 is a "HIGH" in my code and its working perfectly but my next plan is to put my "actual probe setup" in my "actual 1000 liter overhead tank" and then read values. I will run it on different intervals and log the reading in my laptop just to see if there is any big change in readings and then I can fix which value I should put to get a "HIGH" correctly every time.
By the way 700 is way to high when the probe is completely submerged in water ..its a huge difference.