I asked the warranty rep. the same question and it was explained to me like this: my pool was built and plastered this past winter. Because of the lack of warm temperatures, the remaining moisture on my gunite prior to plastering did not evaoporate. Therefore, a few months after my pool had been plastered the moisture that was now between the plaster and gunite was leaching through. The theory was to waite till after the summer to see if the stains finished leaching and eventually fade. Unfortunatley, my stains continued to migrate as depicted in the pictures. So instead of waiting till the end of summary, the PB ended up draining my pool and conducted an acid wash. After such, the pool shell was allowed to air out for two days. Given that Houston had several straight days of 100 degree temperatures, the plaster should have sufficiently dried out any remaining moisture. I tried to research this phenomenon, but there is very little literature on this type of stain. Whatever the stains were, they were ugly. Hope this helps.