Its time to open the access port on your tank ... and manually clean it out.
once you become 'infected' (cladosporium resinae, etc.) and there is a deposition of crud on the tank walls, the ONLY way to resolve any and future problems is to get inside the tank and scrub it with a long handled brush or power washer, etc.
Its too late for 'polishing' or 'magic potion' addition. Polishing wont remove the gunk adhering to the tank walls, 'magic potions' will release 'some' of the deposition but will leave some of the resins (including some viable spores). C.resinae forms soft deformable particles that will rapidly choke the typical filter cartridges plus under increased pressure differential across the filter will extrude through the filter media .... only to form a 'coke' in the exhaust manifold and injection elbow area restricting the exhaust gas flow.
The best solution is mechanically clean/scrub the tank internals then add some oil and recirculate polish that ... then simply 'recomission' the system. Then buy only clean fuel (from truck-stop, etc.) and keep only enough fuel in the tank to satisfy your immediate needs plus a little extra for 'reserve'. Dont keep the tank unnecessarily/needlessly 'full', empty the tank for long-term /winter storage. Check the O-ring on your deck fill port.
