There's quite a big gap of air in-between, I think the oxygen is fine.
Won't changing the water everyday stress out the fry? Cause it's really easy to push them around, lol.
Oxygen doesn't magically dissolve into water. It's highly unsoluble in water and therefore needs "water surface movent" to enter the water. What surface movement does that breeder box have?
You know, I've kept fry in breeder boxes for months without problems, but my routine was to flush(pour tank water into it) 2-3 times a day, whenever I have a chance, once in the morning and evening at least. The fry don't get stressed if you pour the water slowly. I just scoop some from the tank and pour it in. And I've had no losses with my guppies or corys. I even setup an air line the last time to make water flow from the trickle filter directly into the breeder box for constant flow. And I got 100% success with cory fry that people seem to have a problem keeping alive for some reason.
Whether this is one of the reasons or other reason for success, I don't know but based on what I am coming across around this forum I am inclined to believe people don't realise the importance of oxygen.
Recently, after setting up a cory fry tank I noticed one day the shrimp going to the surface at night and my cory fry shooting to the surface quite often. I started the tank with a big sponge filter connected to a powerhead with a spray bar. I measured ammonia/nitrites-none, then I added an air pump. It wasn't two hours afterwards when I had a bunch of playing little wigglers that barely went to the surface anymore and became quite lively. Then I thought I was imagining things and I disconnected the air pump a few days after because the tank is planted and I didn't want the air pump diffusing the CO2 out. It took about 2 hours after that for the corys to start shooting to the surface. Besides that, they were listless and staying not moving much. So how do you know oxygen levels are ok in a small box that gets little to no water movement?
I also got one of these hang on breeder boxes that pump water from the tank constantly via an air pump. There's a warning in the manual to be careful with the amount of fry due to possible oxygen deprivation if there's too many in it. And that's considering water is pumped 24/7 into this thing. In a normal breeder box, there's barely any flow and therefore oxygen levels can go down in no time. Hence people always wonder why their fish die all of a sudden with no signs, especially fry in tanks with little filtration, weak sponge filters, etc...
I am not saying that yours died because of that. Based on my personal experience with low oxygen levels, which happened in my adults tanks as well on several occassions over the years when not setting up the filter output correctly, people to take into consideration that oxygen is the first important thing, same as for humans. Fish get highly stressed and die with low levels of it and is a mysterious killer number one. It's needed for the filter bacteria to function, for organics to dissolve into non-harmful substances, etc....and these processed compete with the fish for oxygen. Unless you measured the oxygen levels somehow in that still water breeder box, you can't say oxygen is enough. Even the net type breeder boxes are known to gather tiny debris and slime on the outsides making the box work like a mini, non-cycled tank if not cleaned.
Sorry for my ranting.
marks, but today, about more then half of my little baby platy's have dropped dead! I have no idea why, either! They all looked healthy, even started to get more colour. I just look in every now and then, and yea, a couple I was sure would die at some point, but in the same day, 5-6 of my babies has died!! I only had eleven, and now it's gone down quite a bit. 
Please help before I wake up in the night and they are all gone!
