To fix this issue long term, you need to figure out the boil off rate of your boil kettle, and figure that amount into the overall water volume calculations. Boil off is a constant factor of time and surface area, so boil like a gallon of water in your pot for 15 minutes at the same "vigor" as you normally would, measure the amount of water you lose, then mutliply that by four, and you have your per hour boiloff rate.
Primary #1 - Midnight Ryeder (Midnight Wheat and Rye)
Primary #2 - Florida Weiss
Primary #3 - Kane-DOH APA (Honey Citra APA)
Secondary #1 - Downtown Flanders Brown (brewed August 2012)
Keg #1 - Raspberry Florida Weiss
Keg #2 - Cinnamon Raisin Cider
Keg #3 - NONE!
Bottled - NONE!