Our panda cory cat looks really sick. I just checked one everyone and his gills look bloody and red and his fins look bad too. He's also breathing heavily. He's in a 10 gallon tank (sand and minimal gravel substrate) with 3 male guppies, one leopard cory, a snail, and two peppered cories. The temperature is 78F and constant, ammonia 0, nitrate 3, nitrite 0 at the last test a few days ago but I'll test again just to make sure. We change the water every five-seven days. The tank has been set up for 3 months and is completely cycled. Does anyone have any ideas? His gill on the other side looks completely normal and he was fine yesterday.

