Well, Sorry I forgot to say. They told me that it was an alligator gar and judging by the pic of the alligator they're correct.should be good until it hit 15-16'', depend on what species of gar that tank will last from 6 month to a few years(considering the gar is now about 6'').
How big is the gar right now? Read this sticky http://www.monsterfishkeepers.com/forums/showthread.php?406951-Gar-Species-Profiles-(1-Viewing) and tell us which gar does it look like!
I've never heard of young gator gar put in 4'' a month! the fastest is about 2-2.5''!Alligators grow extremely fast if fed properly. So that 6 months could be more like 3, haha.