How long do you have to keep doing that cycle of treating?
Does DE work? I read that it kills mites?
Unfortunately DE is not an effective treatment for a mite infestation.
You will want to break the cycle, so repeat treatment in 5-7 day intervals until the mites are gone.
There are different types of mites, that's true. Most mites have a life cycle (from egg to hatch) from 5-12 days, depending on type, weather conditions, etc. So treating in a time frame of every 5-7 days will help break the cycle.
Make sure to treat all the nooks, crannies, crevices, roosting bars, nesting boxes, ceiling, etc. of your housing.
For treating housing, I like to use Permethrin Spray it's easier to apply and spray into corners, onto walls, etc. The concentrate is also economical and will last a long time, you just mix it up as needed.
For the birds themselves, I like to use dust. Place the powder in a sock or knee-high hosiery, then gather up your bird, tap the sock onto the feathers releasing a fine dust, making sure to get around the vent, under the wings, etc. I usually just tap all over and make sure to rub the dust down to the skin. The sock helps you control the dust and where it goes. At least that's what works more me. I then just store the sock in a jar with lid so it stays dry and out of the way. If you are doing a number of birds, then you may want to wear gloves and a mask. I usually only treat a bird or two at time, mainly broody hens or individual roosters, so I'm not breathing in much at one time or handling it a lot.
Anyway, that's my 2¢