I just topped off for winter storage. I have the 5411; 15 gal? diesel tank. I used 7 gal since last October. Should I use a maint dose of biocide for all 15 gal? (last year I only used a half tank also and treated the whole 15 gal. ALSO, I did a double dose of fuel STABIL. It prevents varnishing and removes water condensation. I treated the whole tank last fall and again this spring. It seemed to start easier this summer. Was able to cut my glow plug warm up time by 1/3rd. I plan to treat the whole tank again now that I replaced the 7 gal. HOW MUCH IS TOO MUCH??????????