I just read through 6 pages on another forum about the stuff. Seems white egg crate IS a major problem! The folks there are now washing, bleaching, soaking in vinegar, and then spray painting their egg crate with Krylon Fusion black paint.
90% of the people that responded all said they had this tan algae form immediately despite their perfect tank husbandry. I will wipe it off, and the stuff is back in a day. I think I will find another way to hold my chaeto algae. Any ideas?
The consensus is that this is only a problem for the HomeDepot and Lowes egg crate, as its made of polystyrene and the new manufacturing methods use both phosphates and other odd stuff to help release the egg crate from the molds.
Seems the best way to stop the algae is to paint the stuff.
Maybe I will have to look into acrylic afterall, as I dont want to play with bleach and vinegar and whatnot and then spray paint.