This is one of the very few times that I will ask a question about a swordtail. I have been raising them for years and I have pretty well mastered the concept of raising and breeding them. My only problem is raising the fry. Now, I have a bunch of red wag and painted sword fry. Several were almost large enough to go into the tank with the larger ones.(this would have been a first for me) Unfortunately, several days ago, I started losing some. I have them mixed with platy fry, but the only ones that I keep losing are the sword fry. I believe that I have lost about 20 in the last five days.

I wanted to take water in to get it tested, but I have gotten the flu and haven't been able to go anywhere. Even then, I know that swords and platies have almost the exact same DNA, so why is it that only the swords are taking the hit from these mysterious deaths?
Any advice would be appreciated.
Thanks.