Building a sump and trying to estimate how much back flow will occur in a power outage. The tank will be about 140 gallons and if the water level drops 2" will lose 15 gallons to the sump. My planned sump could only handle 13. But, if water levelin the display dropped by 1.5" It would work. So just seeing what happens in everyone else's tanks. In my current 75, the display only drops an inch in a power outage, but my return pump is not very strong which explains that.