Winterizing a pond my spouse pulled a big filter with something that looks like plastic balls. What do I do with these over the winter?
Those are the working part of your bio-filter. Let the water drain out, put them in a garbage bag and store them somewhere dry. Next year, you will need a new box of them. They run about $60. Take half of your old ones and put them in with your new ones. I was told the bacteria lives for a long time in them.