last night a silver Danio suddenly died and this morning a male platy sudddeenly died. Both acted normal right up until they died. I had actually looked at my platy and he was fine stirred my kraft dinner and went back and looked again and he was dead. no physical sign of illness on either fish water changed about a week ago (complete overhaul) levels and temp were all same as before I changed the water. any ideas what else could be causing this? Platy was fairly large so possibly Old age?