Also, clones or from seed? Spider mites can hitch a ride into your room on clones from somewhere else. They also can be in soil in the form of eggs if your not using sterilized soil. Are you around others grows or other plants in general before you enter your grow? They can hitch a ride in on you. Pets? Same thing. Nothing should enter your room without a good cleaning, including all tools and yourself.
Treat your room like a bio lab, and go out of your way to keep things and yourself clean and you will minimize your bug problems. Figure out how they got in and try and prevent it in the future...But sooner or later, every grower will get spider mites. Some say experienced growers don't but that's bullshit. Everyone gets mites.