I am currently running my sump (30 Gallon) around the 12 gallon mark when the return pump is in operation. When the return pump is killed the sump will backfill to about 15 gallons. Leaving something like 15 gallons of water volume I could use not being used. Any reason why I don't increase it to something like 18 gallon mark when running, 21 gallons when the return pump is dead, and 9 gallons of safety? What do you do?