I have been using allergy filters in the home HVAC for years. Several household members and a cat are sensitive to air quality. Last year the filters I used were no longer available. I switched to a 3M Filtrete 2800 Ultrafine Filter. These are pricey. When I was at SAMs I purchased Filtrete Allergen 1200D which I used during the winter. Due to concerns of restriction if too dirty replaced every 2 months. Fast forward to today. In March a Air Scrubber was installed. The technician said run the blower motor 24 hours a day and that was what I have been doing. I thought I will just replace the filter after a month. I had a 2800 filter in a month and replaced it with 1200D. Next day cat was sneezing all day. I noticed a lot more allergies and had a hard time keeping them calmed down. This continued three days. Put old filter in and now cat is fine and I am fine. So I was told to only use the 2800 filters. Looks like current price is $30 each. Do not want to replace them too soon or too late putting stress on the HVAC system. Looking at this air filter gauge at Amazon, but has mixed reviews. General Aire G99 Media Air Cleaner Filter Gauge What do you think? Thanks in advance for your guidance!