Sick angelfish?

We have a single angelfish in a 10 gallon tank. She's about 2-3 years old. Today she is sitting at the bottom of the tank and not really moving around and she didn't eat when i fed her. This is very unusual. Do ya'll have any ideas of what could be wrong?

Thanks!!

Welcome to our forum. A ten gallon tank is pretty small for an angelfish. In addition, small aquariums need very careful maintenance, because any toxins will be more concentrated than they would in a larger aquarium. Angelfish also need a water temperature around 82 degrees. Lower temperatures will slowly wear them down and shorten their life.

and also there may be high nitrate or ammonia value,so the best way is you should take a part of your aquarium water and check it from your nearest aquarium shop whether it is ammonia or nitrate free or not.

Thank you, I'll take a water sample by tomorrow and see what all I need to do.