How can you tell if a molly (fish) is sick?

Question

I have 4 mollies and 1 of them is looking ill. I was thinking he was stressed, so what can I do to un-stress him? Also, how can you tell if he's sick or not?

Answer 1

you can see if it's not eating, if it's spacing out, which means it swims fast around and doesn't rest as example

if it is stressed, make sure your parameters are impeccable which means

0 ammonia and nitrites

and nitrAtes should be kept below 20 ppm