You could try sand but I don't think it will do much for the smell. The birds might enjoy using it to take a dirt bath or may eat it as grit. I would start with cleaning everything out and starting fresh. Put down a layer of shavings first. Use pine not cedar. While cedar is good for the smell, the scent can be a bit strong for the chickens. Sprinkle the DE on top of the shavings then put a layer of straw. It doesn't have to be a real thick layer. Make sure you avoid inhaling the DE and try to keep the chicks away from the dust cloud. It isn't toxic or anything. It can irritate your eyes just like dirt can. The DE has a drying effect on things too so it may help absorb some of the moisture which causes the smell. Someone in this thread also mentioned using lime. I have never used that so I can not say if it works. You can leave this base layer down and just sprinkle fresh litter and DE. I haven't changed my run litter in about a month and just did my coop today. Did the coop because it was starting to have a little smell. The key is to keep things dry. If the litter is too thick then it can't dry out, especially as it gets cold. Hope this helps.