during midnight some angelfish appears at the surface looking as if it is "Gasping" for air
First thing to check is your parameters. Gasping at the surface often is an indication of a problem with your water.
Ammonia and nitrite (with an "i" need to be at 0ppm
Nitrates should be under 40ppm, its better if they are under 20ppm.
Temperature should be suitable for your fish.
And make sure your Ph has not changes rapidly lately.
A water change may alieviate their stress though it is helpful to know your parameters so you know how much to change and how often.
Also make sure you have sufficient oxygenation of your water -- either a bubbler or your filter splashing water a bit.
Gasping for air at the water surface could mean the angelfish has ammonia poisoning. Ammonia is a byproduct of fish digestion and respiration, and it will burn gills and weaken immune systems. To see if ammonia or other toxic nitrogen compounds are the problem, test the water. Ammonia and nitrite should measure zero, and nitrate should be less than 40 ppm.
If toxic nitrogen compounds are not at the levels listed above, start changing about 25 percent of the water every other day until they are. After that, change 25 percent of the water every week, and always feed no more than the fish eat in a couple of minutes.
In a healthy aquarium, the nitrogen cycle takes care of the toxic nitrogen compounds. It works like this:
Two of us were responding to your question at the same time, so please excuse any repetition.
Your reponses are always welcomes especially since they come from experience instead of booklearning -- (like mine are) Never appologize for adding something. In fact I find that sometimes if several people repeat the same information, people take it more seriously (or trust it more)