http://www.algae-x.net/Algae-x%20Binder/LGX%20Binder%2017.htm

This stuff is used by many owners/operators of diesel powered sport fishing boats in that I knew when I lived and worked in Florida. Almost all swore by the additive and most used the magnetic device also.
The price for the additive 8 oz. for $25.00 treats 320 gal. = $1.56 per 20 gal. tank full.