Go,

Its not algea, its fungus. Algea grows in the sun and is green, fungus grows in the dark and is brown.

You don't have to clean out the tank, but you may have to replace a couple of fuel filters. You do have to clean the tank strainer, though.

I used Biobor and only plugged one inline filter and that was a year ago. So it all depends on how much fungus was in your fuel system as to how many filters you have to replace.

P E H