Well, it's back to square one for me. As of today, the last two otos are dead. Thankfully, I only had to euthanize one other one myself, but the whole situation really really sucks.
So I'm going to drain the 12-gallon tank, scrub down the plants and cave with hot water and an algae scrubber, and start cycling it again. I'll medicate it like there are fish there, and let it run for a week or so before getting new otos. And (on the advice of my darling hubby) I think I'll get the next bunch from the awesome fish store in Wilmington, rather than from PetSmart again.
I'm not saying PetSmart is at all to blame here - of course not! All blame is always on me in my own house/mind, and this year *everything* is my fault (thanks Sand and Barbara for that honor!). The otos in Goldie and Alfie's tank have been doing well for quite some time now, and they're all from PetSmart. I just need a whole new beginning. Plus, I really like that store!
I do have to mention this oddity: up until now, whenever any of the otos died, their bodies either disappeared (probably eaten by the goldies/Bill) or sank to the bottom. I thought this was odd, since dead bodies are supposed to float, but chalked it up to some possible aspect of their physiology. BUT *these* two little guys are floating, and strangely - they are totally vertical! One is at the top of the tank with his nose just barely poking out of the water, and the other is at the bottom of the tank, standing on his tail fins. What the HELL? I'd post pics (because it is strangely fascinating), but that would be disrespectful and morbid. But it is just SO freaking weird. Sad, but weird.