Ever since these fry were born, some of them have black edges around their fins. It has not gotten worse, and they have been active and healthy.
I called a friend who breeds swordtails now and then, and he said that black edges on fins are a sign of recent swordtail genetics. This would make sense, since the fry are platy/swordtail hybrids.. whoops.
The ammonia levels were apparently high (.5 -1), but since the fry have been alive and well for almost a week, and the shrimp are as active as always, and I did a 25% water change twice this week to make sure. So, I think the ammonia reading may have been wrong.
Help would be greatly appreciated!