The black angelfish in the picture has excess mucous on its body and pectoral fin. This is the cream/ white film over the fish.
Fish naturally have a thin layer of clear mucous over their body to protect them from poor water quality, external parasites and disease organisms, and to help them move through the water easier. When they are stressed out by something, they produce more mucous and it can appear as a cream or white film over part or all of the body and fins.
Poor water quality (ammonia, nitrite, nitrate) is the most common cause of excess mucous.
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Test the water for ammonia, nitrite, nitrate and pH.
Wipe the inside of the glass down with a clean fish sponge.
Do a 75% water change and gravel clean the substrate every day for a week. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.
Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.
Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.
If there is no improvement after a few water changes, post the water test results here and add some more pictures of all the fish.
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Don't worry about the white poop at this stage. It's probably internal worms but the excess mucous is a bigger issue and will kill fish much faster than worms do.