My Kreepy Krauly 820 is about 14 months old and has started leaving a trail of dirt behind it along the treads path. The pool filters have just been cleaned so I don't think that is the issue. It still picks up a lot of dirt but it is not doing the amazing job of keeping my pool spotlessly clean that I am used to. I live in the desert so a lot of dust and dirt gets deposited on the bottom of my pool. Do the filters in these units need to be replaced this soon or is it something else that causing this? Thanks in advance for any advice.