ok. Had the poly sitting in bleach for a little bit now, but I had another idea come to me while I was doing dishes.. I have crappy tap water... I found sand on my dishes in the dishwasher so the stains could very well be sediment collecting in the poly.. The
nutrient is being sprayed onto the poly with a small bit of force, so I am thinking the poly could possibly be working as a sediment filter catching the dirt and crud.
I am going to leave the bleach on the poly over night to see if I notice anything else