There is what looks like a semi solid stain on that deck now, if you plan on applying a transparent deck stain all of that material has to be removed. Cabot, Benjamin Moore, and most of the major paint companies sell transparent oil base deck stains. If for any reason you can't remove 100% of the coating you can use a solid deck stain over that, it will be a coating that will need to be re-coated every year or two, if you're lucky and do a good prep job. Anything but a transparent oil based deck stain imo is a mistake. Keep in mind if the deck faces north and has tree covering, oil base stains are a breeding ground for mold and mildew. No worries about low VOC, I doubt you'll be able to find anything that isn't.