Well, I think I'm done with otos. I bought 4 of them at different times from different fish stores. Drip acclimated them for two hours and my water parameters are stable. I found only 1 body. The last one that was alive has now disappeared with no body.
I've never dealt with such a sensitive fish before. And I can't even find the bodies to take them back with a water sample. Fortunately the apple snails are making quick work of the diatoms.