If the fish get plenty of plant matter in their diet, they can eat a normal tropical fish food. They should get live aquatic plants as part of their diet regardless of what they are fed.
The fish in the picture in post 11 appears to be dying from poor water quality (ammonia). It also has black edging to the fins, which is often associated with ammonia burns. However, the black could also be colouration but I don't think it is.
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BASIC FISH FIRST AID
Test the water for ammonia, nitrite, nitrate and pH. Post the results in numbers here.
Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.
Do a 75% water change and gravel clean the substrate every day for a week or until the problem is identified. 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. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
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 the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.
Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.