Help Please

[resolution]

All of a sudden all my fish have started to die. Cleaned the undergravel filter, changed the heater, regular water changes have not helped. introduced new fish a week ago, regular supplier of community tank stuff we hve used before - 6 black widows, 10 black neons and 6 platy - all dead, apart from black widows. Although have had tank some considerable time (6 years I think) we are by no means experts and have always just muddled along. Why is it doing this now. Nothing has changed as far as we know.

any suggestions would really be appreciated.

 

[bobf]

All of a sudden all my fish have started to die. Cleaned the undergravel filter, changed the heater, regular water changes have not helped. introduced new fish a week ago, regular supplier of community tank stuff we hve used before - 6 black widows, 10 black neons and 6 platy - all dead, apart from black widows. Although have had tank some considerable time (6 years I think) we are by no means experts and have always just muddled along. Why is it doing this now. Nothing has changed as far as we know.

any suggestions would really be appreciated.

First place to start is a water test kit - need to check levels for Ammonia, Nitrite, Nitrate Ph and hardnes levels.

Was the tank cycled?