It sounds to me as if Carl is right and you've got a great pool on your hands. The only thing that sounds fishy is that a 75 sq/ft DE filter would be positively huge for your pool and it would take much more than 4 of the small sized coffee cans of DE to recoat it. I'd bet you've got more like a 40 sq/ft filter, but that's still plenty for the pool. You should check into this because you'll get a much better result from using the correct amount of DE.