Ph down on seedlings

I guess you could, but would ask why you feel the need to do so.? Far better to let your delicate babies establish themselves before messing with them. At this early stage of life, it is far easier to cause them problems and/or damage them, as they are trying to figure out what life is all about and make some roots. If you really want to do something your seedlings will appreciate, try watering them with chlorine free water. This can be made by just filling a bucket with tap water and leaving it to stand, uncovered, for 12-48 hours before using it. This timeframe will allow for most of the chlorine and any other chemicals in the water to evaporate off and leaving you with superior and cleaner water that has far fewer chemicals in it that could upset your babies. It will also be "room temperature" water, which never is a bad thing with gardening in general. Hope this helps.... Organoman.