Take into consideration the airflow reduction in any filter medium you use.  Also consider how much filter surface area you need in order to accommodate your CFM rate.

Pocket filters are best for high airflow environments.  Most air filters will state in fpm.

Example from Google:
Select air filter dimensions (length, width, thickness). 2. Calculate airflow velocity in linear ft./min. using air volume rating of fan in cfm divided by surface area of air filter in sq. ft. (i.e. 200 cfm./0.50 sq. ft. = 400 fpm)

If your CFM is higher than the capacity of the filters they will loose efficiency and essentially stop filtering.  The more the discrepancy the more they don't work.

Most people vastly underestimate how much filter surface area they need for a bitcoin mine.

Also consider the added resistance the filters add when considering fan size / quantity.