Swordtail Fry Randomly Dying

[Spookie]

Hi! A female swordtail fish gave birth to a batch of fry about 2-3 weeks ago in my 15 gallon tank. All were fine, I counted about 9-10 up to a few days ago that were easily spotted. Suddenly, yesterday, I could only spot two. Tonight I see none. They are in a community tank with other full sized mollies/platies/swortails, but are never chased around or eaten - the others lack interest in them and there are many hiding places and plants for the fry to hide in. I had tested the water earlier this week before any problems arose and all parameters were normal, I tested again tonight and they were the same. No adult fish are suffering from any sickness... though I did have a 3 month old black swordtail fry that suddenly also disappeared around this same time. One other fry I have around that age is perfectly normal and fine. Any clues what could have happened? Thanks

 

[Aron]

I know you said they don't get chased around and eaten but it is amazing what happens when the lights are off! That's one possibility, the other is they have gotten better at hiding!? Also, make sure they can compete for food, without it then they just may have been weak and the slightest indifference in water quality has killed them.