Thanks, all. I do not know the exact cause of the fish kill. From all the research I've done and the symptoms of the dead/dying fish, I assumed it was disulfuric acid??? that was released after turnover. I've tried but failed to find someone in my area to do a water analysis. I did have more FA last year, due, I think, to the cold, wet spring we had. I also get a good share of leaves blown into the pond. I'm just shocked at how completely changed this pond has become. It is still what I consider young, being built in the fall of 2012. It has always been teeming with aquatic life. Now, we see nothing but a couple turtles and bullfrog tadpoles--no fish or frogs at all. Its color has been off since last fall's event as well. It always cleared pretty quickly but now has a kind of milky, dirty hue to it. It receives good drainage and fills quickly. Regardless, I need to decide soon whether to restock and start over--or not. If the water is bad, the restocking would be foolish.