Tests all looked fine, btw, no need to do the high ph unless the regular one maxes out. To treat for parasites, you first need to identify what kind you have. I would start off by adding air pumps, and air stones, to add extra oxygen. Set up your quarantine tank, or a large tote, fill with pond water. Gentley catch a fish, put it in, look it over. You are looking for any sores, missing scales, red on fins, tail, or gills. Any weird blobs, worms hanging on them. If you can’t find anything on that fish, look at the others. We don’t have enough information at this time to say you have any particular problem other than one fish died, which could have been due to a congenital defect.