Fish Dying?

[Stina]

Hey I have a question...I have a freshwater community tank it has been up and running for a few months now...I didnt have a heater at first cuz I didnt need one but then it started gettin colder and the water started getting colder so I got a heater and slowly raised the temp of the water to 78 or 80 degrees where its supposed to be and my water conditions are perfect but now all of a sudden I just randomly have fish dying out of the blue...does anyone know why this might be happening or what I can do?

 

[Chad]

It could be related to the heat. Heat can change the pH of a tank which if done too quickly or drastically can harm many fish.

 

[PrairieSunflower]

What type of fish do you have? Maybe the temperature is a bit too high.

 

[Bugdozer]

The higher the water temperature the less oxygen the water holds as well. Are any fish gasping near the surface?