Question is how much are you feeding them? Do they have enough to eat since there are so many of them in one tank? The other factor is the strength of the air stream. I am only guessing here but how often do you change the water? For this many fry in a small tank, you will need to replace water every day if not every other day if you feed them a lot of food. This is my take on this.
1) Have a 5gallon bucket set aside with water treated for chlorine ready
2) Siphon off 15% or 20% a day and replace with fresh water to keep tank clean
3) feed the fry with newly hatched brine or fry food so they all have a chance to eat. If not well fed then the stronger or larger fish will out do the weaker ones.
4) check to see if the air bubbles are coming through too strong. This may cause the fry to be stressed out and die
Let's hope you don't loose much more and curious as to what they will look like when grown.
Good luck!