Fuel polishing only, with an obviously fouled tank ('brown/black' fuel) is a total waste of time, money and effort, as polishing will not remove the accumulated alkenes, etc. and fungal cellular fragments adhering to the tank walls. Traditional industrial, etc. remediation requires that the tank be thoroughly cleaned ..... THEN you recirculation filter polish to remove any residuals.
There are some recent 'improvements' to such remediation that may be of benefit - IF you have access to a transfer pump, an INDUSTRIAL filter housing (with a graded pore depth media filter). ..... AND one of the newer 'enyzmatic TANK CLEANER" Compounds. You want a large capacity pump (for the highest possible volumetric 'turnover' at approx. 3-5 gallons per MINUTE), 2.75" dia. X 10" length graded pore density depth filter @ 10-15µM (or larger). Add the Tank Cleaner, let sit a few DAYS, then recirculate the fuel for several HOURS/DAYS through the /pump filter set until the fuel becomes 'visually clear'. You may need to change to a 'fresh' filter several times (such filters only remove ~50 grams of 'crud'). The HIGH turnover rate through the filter for a LONG time will eventually remove the particulate; but, you 'may' need to 'final trim' the particle load with a 2-5µM depth filter. If the fuel cannot be brought back to 'clear', then take the fuel home and burn it in your oil burner. Add more fuel and more tank cleaner, etc. etc. until the fuel becomes 'clear' druing the recycle process. You should be able to rent such a transfer pump and filter housing from a tool rental. If you cant get graded pore density filters then go to Home depot and get some polypropylene 'spun bonded' ~15µM (and maybe one or two 2-5µM filters). This is going to be a long particle extraction process
Recirculation polishing a fouled tank will be of absolutely no benefit in 'cleaning' a tank; however, an onboard recirculation polisher (always operating when the engine is on) will quickly bring the particle population back under 'control' if/when the tank 'slugs' itself with particles breaking loose from the tank walls. Once a tank is cleaned the BEST method to keep it clean
is an onboard 'constant run' recirculation polishing filter.
Recirculation polishing WITH an enzymatic tank cleaning compound will probably be of great benefit. Better to mechanically scrub/clean the tank .... THEN recirculation polish AFTER tank cleaning.
Tank HAS to be cleaned, either by mechanical scrubbing or by enyzmatic Tank Cleaners.
fouled tanks .... dont top-off your tanks, keep onboard ONLY the fuel amount you NEED plus some reserve, dont get your fuel from a 'low turnover' source such as a MARINA - get it from a high volume TRUCKSTOP etc., use an anti-fungal compound, clean out the tank on a routine maintenance basis, install a small onboard recirculation polishing filter.
Example of 'tank cleaner' .... http://www.starbrite.com/productdeta...&ProductSSCat=