Actualy, 'black tetra' can encompass several species (mainly black skirts/widows, black enons but sometimes black phantoms etc). Black skirt/black widow tetras are common names specific to a single species (gymnocorymbus ternetzi). Black skirts get to 2" and are the wrong shape to be eaten by angels. however, they are known nippers so are not the best fish to keep with something that has long fins like angels do.
As for the temp. thing - lowering the temperature may reduce aggression in that it discourages the fish from breeding. Angels are most aggressive whilst breeding. It also reduces their metabolic rate and, therefore, activity levels. however, this is stressful for the fish if taken to extremes and it's not a good idea to do this kind of thing when you can, instead, simply ensure you are keeping compatible fish. Also ntoe that aggression is not the reason angels eat small tetras just as predatory species of fish don't attack small fish because of territoriality/aggression. They simply view the small fish as food.
As for the temp. thing - lowering the temperature may reduce aggression in that it discourages the fish from breeding. Angels are most aggressive whilst breeding. It also reduces their metabolic rate and, therefore, activity levels. however, this is stressful for the fish if taken to extremes and it's not a good idea to do this kind of thing when you can, instead, simply ensure you are keeping compatible fish. Also ntoe that aggression is not the reason angels eat small tetras just as predatory species of fish don't attack small fish because of territoriality/aggression. They simply view the small fish as food.
