Several updates, and some questions below.

Water quality update: Water continues to be extremely clear, actually getting even clearer as the season progresses. We can now see a rock pile and a barrel that were placed in about 8-10' of water. I had our water chemistry tested at Penn State, and here are the results:
  • Nitrate: 0.8 mg/L
  • Phosphorus: <0.025 mg/L
  • Total Dissolved Solids: 33 mg/L
  • pH: 7.2
  • Total Alkalinity: 8 mg CaCO3/L
  • Hardness as CaCO3: 17 mg/L
  • Iron: <0.1 mg/L
  • Manganese: 0.05 mg/L
  • Aluminum: <0.03 mg/L
  • Sulfate: 7.0 mg/L

Questions: Any thoughts on the water quality/chemistry? Should we add ag lime, and how much per acre, given that pH is fine but that total alkalinity is quite low (I think)? Penn State's guidelines say that our pond's manganese is high, so is that an issue for our fishery? If so, where could manganese come from (soil?), and how to reduce it?

Feeding update: Perch are now feeding incredibly well. Our remaining adult bluegill have pellet trained themselves, so we regularly see a few BG show up to feed. I have to feed most of the way around the pond as the YP have spread out and constantly wander, and in most spots I can throw in a glob and get a response. We've ramped up from feeding about 4 oz. per day (by volume, measured as dry pellets) to now 12-16 oz. per day.

Survival update: We had a steady trickle of YP dying over the first two weeks after stocking. I saw/confirmed 12 dead (out of the 150 stocked). Then, we had no new dead perch seen during week 3. Now tonight, after feeding, we saw 1 perch come up floating, belly-up, and he had the energy to try to swim and flip himself rightside-up, but for some reason he couldn't flip over. I assume he will also be dead shortly, so now we're at 13 "confirmed" dead. This particular perch came up in an area where we had just pellet fed heavily, he had quite good body condition and the blue tint that pellet eaters have, and the school in this particular spot was (abnormally) eating lots of pellets off the top (ours usually only eat sinking pellets). I saw this same belly-up behavior with 1 other perch that died a couple weeks ago. I want to figure out why he died, because we paid good money for these fish, so it would be nice if a couple actually survived.

Questions: What are some potential reasons why these YP died, especially considering the strange behavior of floating belly-up while still apparently being strong enough to swim and try to flip over right-side-up? Could it be that he gorged on pellets and they're just buoyant enough to make his belly/underside be too buoyant? Could it be that he was eating too many off the top and gulped too much air into his stomach? Could I have overfed him, and he died from overeating? Could it be my pellet hydrating technique (hydrating in ziploc bags using well water)? I also squeeze my pellets into globs about the size of a ping pong ball before throwing in, so the pellets from each throw are concentrated and sinking in a tight formation, which means that the school has to be a bit competitive/aggressive, so could this tight formation and "fighting" over pellets stress fish too much to the point of killing one on occasion?