Can Gh be lower than Kh?

Just picked up an amano shrimp for my Nano shrimp tank to eat the little bits of hair algae that I have to pluck every couple months (it grows super slow so the tank is well balanced). The water from the fish store is testing at 3dGH while I'm getting 4dKH. I personally have never seen this with any of my tanks and was wondering how could this be possible? Is it just because they might have a different type of carbonate in the water that isn't read by the GH test? Is my test going bad since I've had it for about 10 months?