Here is a link to: Filtration Tips is published monthly by: Noria Corporation, 1328 E. 43rd Court, Tulsa, OK 74105 USA. (918) 749-1400 I get this monthly and it's free to sign up for and the site has a lot of good info. Hope it's ok to post here and that you find it useful. http://www.filtrationtips.com/2006_07_12.htm John & Susan MV "MARIAH" living aboard (Simpson Bay Lagoon, SXM) Gwynn's Island Trawler,62 http://makeashorterlink.com/?A26A5224C