3 dead fish

Was the tank cycled and did you add all 6 fish at once? If the tank wasn't cycled this is what likely killed the fish especially if they were all added at one time. For either scenerio make sure you do a water change. If cycling is the problem please post and we can go from there. Don't replace the fish for a few weeks until your beneficial bacteria can handle the load of the fish which are in there now.
 
Weekly water changes are necessary to keep a healthy tank (generally, 50%). Please post the water parameters I listed, not just the pH. Like everyone said, angels are not a good fish for a 10g tank. They grow about as large as your outstretched hand.
 
smaller tanks are more sensitive to water quality. strange as it may sound, bigger tanks are actually easier to maintain and are more forgiving in water chemistry.
so please consider getting a larger tank if you want to keep angels. a 25 gallon tank wouldn't be all that much larger in footprint, 24x12 versus the 10 gallon being 20x10.
otherwise, for your current 10, several more tiger barbs are all you'd want to keep.
 
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