Why are my platies dead?

[Bindel2303]

I have been having a little bit of an algae problem lately. Not horrible, but worsening. Well yesterday I get home from work can all of a sudden my previously clear watter is cloudy and theres i a bunch of foam collecting by the filter. I had no idea what happened. The only thing I could think to do was a water change, so I did about a 30% water change with water I have had sitting in a bucket covered. When I get home later they are fine, when i leave for work in the morning, they are fine, when I get home My platy and her seven 2 month old fry are dead. What happened? The thing I really don't get is I had a huge disaster in October that killed all my fish except for this platy that survived, pregnant, to give birth 2 weeks later to 8 healthy fry. Now, something that seemed so sudden and not nearly as bad kills her? I'm quite confused. Any one who can help me I would be quite grateful.

[emc7]

I think a water change was a good idea. Assuming you have good water quality (have the water tested, if you haven't yet) in your tank and are conditioning your new water (dechlor), look for something that changed. Who has access to your home? Do you have roommates that overfeed, maids (or mothers) that spray cleaners or borrow your bucket, landlords that spray for bugs? Did you add any anti-algae stuff or water clarifier? Have you ever noticed the heater to stick in the on position? Was the tank warm or cold when you found the fish dead? Was there an odd smell? There are diseases that kill quickly and it is almost impossible to diagnose from a rotting corpse, but usually the sudden death of all the fish in a tank is a water quality issue. It can be normal: ammonia, or nitrite, or some exotic cleaner or pesticide. Did anything happen to upset the filtration bacteria? Did the algae interfere with the filter's operation? Did you treat with antibiotics in October? Did your water supply change drastically (Ask the water company)?