DE and Deep Litter Method don't mix. DLM is essentially a compost system, DE kills a lot of the organisms that make DLM work.Keeping the ammonia down and the coop clean, I have read about DIATOMACEOUS EARTH as a natural treatment for the coop. I got some and also started practicing the DEEP LAYER METHOD that I read about on here. The DE is supposed to help with parasites both externally and internally by adding it to their food. I'm sure there are others here who know ALOT more about this than I do but maybe you should research these two options. Good luck!
Here is a good account of DLM, that in the second year DE additions made it fail. It's great documentation on a long term DLM.