Tough things those Fungi!!
Until quite recently we were operating a Falcon corporate Jet out of a tropical country, and it's tanks were regularly befallen with a fungi-like microbe that would coat everything in a reddish goo...
-even draining the water daily, and doing fuel/water checks on EVERY uplift did not stop the growth..
- even going to a once-a-month application of BIOBOR (recommended is 3 times/year) did not kill the little buggers..
- in the end, the C-check took 2 additional weeks, because they actually had to drop the wing (!) and open the fuel tanks to clean the mess out.
After talking to the people who manufacture the anti-bacterial additives like BIOBOR or Pryst, it seems bacterial growth cannot be avoided in tropical countries, only contained...