Neons & Black Tetra fine--now Platys dying! Help!

[Jififnerm]

My last cry for help was when my Neons were dying with no sign of disease prior to death and no bodies found after. The remaining 3 are fine as is the 1 remaining Black Neon out of 5. But now my Mother Platy has died; again,no sign of illness or distress and the youngest of her offspring ( about 5 months) is missing,presumed dead. The other 2 young ( about 7 months) seem fine,but then so did the others before they snuffed it. Advice/suggestions please.

[WoadCelt]

Heya! I'm sorry to hear about your fish. Its always rough when that happens.

What are your water parameters like? (Ammonia, nitrite, nitrate)