"cottony" Growth On Gavel & Bottom Of Plants

I have done research online to identify the cottony growth in my tank. See the photo. There is indication that it may be a kind of algae, but I can't be sure. It seems to spread, then disappear slowly (but never completely), then comes back again.

I have a 60-gallon tank going for over two years now, and this is relatively now (started earlier in 2010). My current fish include:

4 corys
4 otto's (very new, doing a good job of munching down on the red/brown algae in the tank)
16 cardinal tetras (the hardiest fish I have had!)
5 long-finned serpae tetra
3 bleeding heart tetras
2 killis

I'll be adding some tiger barbs soon (have had them almost continuously over the two-plus years)

Any help in identifying this will be greatly appreciated, so I know for certain how to get rid of it. It hasn't caused any apparent harm to the fish, but its a bit unsightly.

Thanks

Water stats in ammonia, nitrite, nitrate, and ph.
Do you over feed the fish.
How often do you do a gravel vac.
What the temp of the tank.
What filter are you using.
Do you have live plants.
Added any new ornaments, wood, to the tank.

First thing that came to mind when I read your heading is that you may be overfeeding, and the excess foods sinks to the bottom and grows fungus..... It is surprising how little you need to feed and the fish are perfect "con" artists..... when you walk past, they'll come up and "ask" for food.... if you know you have fed them.... ignore their request.