I am a newbie to this, but we moved into a house this past year with a hot tub. Before winter, I thought I closed down the pool properly and put in RV antifreeze to be sure nothing got frozen. Today as I went to open the spa back up, I went to flush the jets and this disgusting yellow “confetti” started to come out of the jets in a large amount. Any idea what this is, and how to prevent it in the future? Thanks for any help!