its filling up a 100 gallon sump so it's probably to much water at one time. It's not like a little bit here and there probably. I'm going to assume that's the problem
The size of the sump should not matter IF the amount of time the ATO runs to top off is within the range BEFORE it triggers the alarm. That is, if it takes 10 seconds each time, then no alarm. If it suddenly takes more thank 30 seconds then you will have an alarm. So the question is what changed to cause it to run over 3x the time. It should not was my point.