Why does the CuLator Ultra 4.0 puff up? The CuLator polymers “hydrate” when they enter the water and puff up. As they bind the metals out of the pool water, the CuLator bags will “shrink” back down to a much smaller size. So, when is CuLator finished? It is easier to tell with the Ultra 4.0 because the bag will be about 1/2 full, or the contents will feel watery inside or they will feel sandy. With the 1.0 it is a little bit harder to tell, but when the bag feels almost empty or there is a lot of color in the bag after a month, then it is exhausted.