I moved up from Syma quads to Phantom 3 Advanced about a week ago. I love it and will have lots questions but the one I'd like feedback on right now is about filters. I planned on getting some ND filters for it but it appears that they screw on and the present one has to come off. I tried it and its on there rock solid. Am I correct in thinking the ND filters are screwed on and any suggestions on getting the present one off? I am thinking a filter wrench but what size would I get? thanks in advance.