FWIW I read your thread and am just out of a similar situation after purchasing from the same set of vendors. I have pegged the issue to bacterial exacerbated by my actions. What got me to a happy place was dosing bacteria (prodibio) and time. Large acros that had no pe for years started coming back to life; made me realize I was likely unbalanced for some time. I lost 1000s. Slowing my roll a bit and I trust no vendor implicitly.So, what’s your best guess on what hit the tank? I did talk to my neighbor who was helping watch the tank. Said he did stick his hand in the tank going after the algae clip he dropped. This was right after he was at water volleyball. Has suntan lotion on and whatever was in the pool and still on his skin. This all started the day after I got back from the road trip. Our pools here are saltwater pools.