scientificaly it should be impossible to gain 1 pound of lean muscle per day..just imagine what happens with 8, 10 or 12 weeks cycles. Although, this is an interesting thread...cause we know most of those 13 pounds are water and maybe some fat, but the important thing is that this short cycle is able to put you on the nex plateau without the need of a PCT. If you keep working out and eating right in the next weeks you'll keep loosing water but you have the chance to take advantage of that gained strenght and keep developing new muscle.