Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Don't wait too long to replace...

The filter definitely works. My son's room was redone and is quite clean (new carpets, new paint, etc.). Yet, run this humidifier every night for a couple weeks, and the filter gets pretty dirty. Forget to replace it for another week or so, and it gets nasty. Forget any longer, and it smells like ___!