I bought my Universal laser in Jan 2016 and have been running it about 40 hours per week cutting mostly 1/8" baltic birch, occasionally cutting acrylic (about 50 hours total since purchase) and about 10 hours max per week cutting 1/4" baltic birch. I have a 3 tier Purex Fume Extraction system and getting an outside blower is not an option. I am pretty certain I need to replace at least one filter but I cannot figure out which one. My gas sensor goes up when I cut 1/4" birch but then goes back down when I stop. My filter also seems to not be drawing the smoke out as effectively as it once did. I read the manual multiple times and cannot figure out how to determine which of the three filters needs to be replaced. The tech support where I purchased laser says all their customers use a blower and they are uncertain. Any expertise out there to help me figure this out for myself? Any help greatly appreciated.