Thinking of buying one of these: http://cgi.ebay.com/HYDROPONICS-6-ACTIVATED-CARBON-AIR-FILTER-18-LONG_W0QQitemZ7756008159QQcategoryZ43555QQrdZ1QQcmdZViewItem For a 6 by 6 ft bathroom would you recommend I buy the 4" or 6" version? Is this unit self contained? What do I need, a compatible fan? I'm confused since I only used a fan with a weak ionizer before but am soon realizing this may be the way to go. Help is appreciated!!!!