I'm confused about what gets washed and what gets replaced, and when. I've washed the pre-filter twice. I'd like to replace or clean the HEPA filter even though the light hasn't come on. The cassette frame - what do I do with it? Clean it? Replace it? The carbon filter I wash. But, how many times can I wash it before I have to replace it? What do I do with the nano-silver mesh? And, where do I buy the HEPA filter? I don't see a place on your website to order it.