Are L102's super sensitive to anything? Lost almost an entire breeding group, everything else is fine.

[alcimedes]

I've had the group for over a year in a 90g tank. It's also my neo shrimp cull tank, and I've got some bronze corys, CPD's and some pygmy rasboras.

I bought some food specifically for L102's from Amazon, prepared according to instructions and put in about a 1" square (maybe 1/4" thick)

they LOVED it. I fed it right before bed because they normally prefer to be out at night, but I saw four at once (when normally I might see one of eight at best)

I get up the next morning, head down to the tank and every snowball pleco is dead and floating.

The shrimp? all fine. the other fish? all fine. nothing else is dead, but EVERY pleco is. (turns out that there's one still alive I found this morning.)

I'm checking with the food vendor to be sure I didn't get some fake batch of food, but I'm stumped as to what would kill every one of them overnight, but not effect anything else in the tank?

ammonia registered in the morning, but there were 7 dead fish in the tank so I expected that. Other numbers looked fine, but I did a 90% water change. (I have a 180g tank next to the 90g that my hillstream loaches are breeding in, so took water out of there.)

Anyone have any ideas? I haven't lost fish like this in over a decade, and I'm really stymied as to what would be so deadly but so specific, especially with thousands of neocardina shrimp in the tank. I'd expect to see them dropping first, or at least with the plecos.