It would seem reasonable to identify the critter (if it is biological)
before you try to deal with it-- many algacides won't work on blue-green
bacteria, for instance.   Just about any botanist at a college or
university can examine a specimen microscopically and tell you what
group(s) of organisms you're dealing with.

(The gentleman who nearly killed himself dumping chlorine bleach
in the crawlspace of his house to "kill mold" comes to mind... seems
he had nice inorganic calcium deposits from hard water evaporation,
and he kept adding more and more bleach and...)

If you don't want to go to that effort, I'd consider removing the
pans, soaking them overnight in detergent and water, rinsing, then
soaking again in 1/10 strength household chlorine bleach, rinsing
well again in plain water, and re-installing.  That should take care
of the current populations of anything alive.

Kay Lancaster    [log in to unmask]