I hope you don't mind me combining two questions in one post.(I'm new).
First I read this post http://www.poolforum.com/pf2/showthread.php?t=1648
several times trying to figure if the problem was actually Brown Algae or Dirt.

I have basically the same problem. The bottom in several spots has brownish/greenish algae/dirt.
If I vacuum it, it appears back the next day.
Not necessarly in the same spot.
I did apply poly 60 and shocked it with bleach. Everything was great for
about three weeks. Now it's back. When I shocked it, the cl was brought
up to around 13.
My question, what is it. That poly is expensive. Should I just try to shock
with bleach. Do I need poly also.
Stats:
29,000 gallons
fc 3
tc 3
ph 7.2
cya 30

Part 2. Came home today, I had thought the kids order some chineese food
and spilled some rice in the pool. Little tiny critters that look like rice were
on the bottom. Not sure what it is. Grubs? Larva? It seemed dead.
It took a while to clean it all up with cart. filter.
Any Idea what it was and how it got there. Hopefully I won't get it again.