Review on Blueair Blue Pure 211+ Lunar Rock Color: Pack of 3 Replacement Washable Pre-Filters by Impresa by Joe Lantz

These three sets are perfect in every respect. Only downside, the "lava" color makes it a bit difficult to see the dust accumulation. The darker color is best for easy viewing and from a distance when you need to erase it. That's the only reason I didn't give 5 stars! If you're using an air filter with the same settings in a room that doesn't have multiple outdoor air sources, all you have to do is mark it on your calendar to have it checked, or simply replace a dirty filter and clean it - no problem. If it is near frequently opened doors or frequently opened windows, these may need to be checked more frequently. All in all a great purchase. If you really want you can use paint to make it darker, that's up to you and adds to the overall cost if you haven't already planned to use some tie dye.