If it is red micro algae (and it doesn't sound like it is) it is preffered by most creatures and slow growing. When I introduced tonga rock I began growing red algae. It is very beautiful and from what I have read and witnessed it is preffered among forms marine life. Red algae grows in low lighted areas and doesn't get as long as the standard green micro algae.

Why I don't believe it is red algae is it normally won't grow on you sand bed because of the low lighting requirments. Mine grew on the side of the glass where rocks shadowed my PC lighting. Your's sounds more like cyano which will commonly grow on the sandbed and also grows rapidly. Macro algae looks more like a plant, micro looks like fine hair, and cyano is slime. above posted asked you parameters because you could very well be dealing with cyano which is referred to as red slime or algae (old mistaken identity.) A picture will help us tremendously even if its a camera phone picture.