I purchased a new hot tub last fall and I've tried two different brands of filters for it. Both have come with an oily substance on the plastic ends. I can see oil residue in the water after replacing the filter and I'm concerned about it. I have never experienced this before with the filters I used for my old hot tub. This tub uses the screw in type filters with the coarse thread 1.5 inch SAE end. Does anyone know what the oil is and why it is added to some filters?