Once a pond is established as yours is the fish dont actually need feeding s there is plenty of natural food in the water, the food we give them only encourages growth, enhances the colour and generally helps keep them healthy. As to how much you feed them it takes a bit of trial and error as all sorts of factors such as water temperature and number of fish all have to be taken into account but the guide I was given was little but often and if there is any left in the water after 5min they had too much. As to the fish the teeny black ones are probably baby goldfish which will gradually change colour