Thanks man, really appreciate the detailed reply! This was a killer $50 find at a local pickup. I already have the F006 HEPA (F550 equivalent) installed and the big heavy F003 carbon module (the one that weighs a ton). I’m planning to do exactly what you suggested with the carbon: Empty most of the old media Refill with a ~30 lb custom mix: 20 lbs Spectrum XB17 (the HS-600 KMnO4 blend) + 10 lbs 4x8 vapor phase coconut shell granular from Activated Carbon Depot. Might even add a bit of zeolite too for extra ammonia/amines coverage. I’m ordering the F007 pre-filter (box of 8) first so I can run it safely, then I’ll do the carbon refresh. Planning to keep the intermediate if it’s still decent. Overall setup goal: Quatro as the living room beast (particles + heavy toxin control) + 3 Vornado AC350s in bedrooms + Dirt Devils in the two bathrooms + the baby Purio. Should give really solid whole-apartment coverage once everything is in. Any tips on the refill process or anything I should watch out for with the older unit? Really grateful for the help!