It is a puzzler. Sorry folks, it was late and I wasn't thinking that most of the details are on my other spawn thread.
The Tupperware was floating in another tank (containing only 6 or so 2.5 week old fry, a 15G tank, filled to a depth of 5 inches). The water level in the tupperware had been lowered to 2 inches to let falling fry reach the surface without Dad there to help. If it tipped, I didn't find any evidence of it, no change in water level. Myates, I will use the plant pots for next time, to be certain about the tipping and to keep it in one place.
There were no holes in the tupperware. I thought about putting some teeny ones in there, but didn't for this go round.
The dad might have been just carrying babies around, but it looked as if he was chewing and swallowing. There had been at least a hundred eggs at a previous check, and only about 20-30 when I removed him. He was still faithfully tending the eggs, but when he saw a baby do it's herky-jerky back to the surface dash, he'd grab it and I never saw him spit one back out or into the nest.
There's no pressing urgency for me to move the tupperware. It can stay floating in there a week and I'll put some green water in there. I'd love if there were a few hiding in there. But without moving the sprig of plant or the leaf, I couldn't see any, even though the tupperware is clear and the night before I could clearly see little eyes and tails all wanting to cling to the surface. I even carefully picked it up to look up through the bottom and from every angle.
It is SO weird. If they died, I should have seen more then just the 3 bodies, right? Either they are REALLY good at hiding or whatever ate them is. I am totally stumped. Is there a kind of flying bug that hunts at the water surface? That's the only other thing I can think of. If it was a water beetle or spider, I'd definitely see it in there.
This is going to drive me nuts.