Honeywell Air Filter Question For My House?

Hi, I have recently installed Honeywell model 2200 air cleaner in my house, and uses FC200E1037 20x25x5 air filter. It says MERV 11 what is this mean? Also how often do I need to change the filter? I have 1500 sq ft house with 2 dogs and adult. No one smokes. But get dusty due to the dogs I suppose. Thanks. OH, and if since I installed this system, do I not longer need to change the previous air filter (22x22x1 in size) nor install anything in there?