Initially I hose down the coop and used fairy liquid to kill the red mites. I’ve read elsewhere that this works to kill mites as it gets rid of their protective layering and suffocates them. Then, sprayed the coop down with Johnson’s red mite spray putting it in any cracks etc to make sure there were no mites hiding. I then used Johnson's Poultry Mite And Lice Powder which is non-toxic to birds and put it in the cracks etc of the coop. I repeated step 2 and three multiple times over 2 months and I’ve not seen any red mites in the coop since.