DE is diatomaceous earth - it is made for the DE filters. You can get it at a pool store, or walmart. It is a very gritty filter medium. You would only need a small bag. If you go to a pool store, can you get a water test? It would be good to see if your chlorine is holding, but a couple of more days of high chlorine won't hurt - you will really know too, if the water clears up with the DE, then the algae is most likely dead.