Slow down leatherback! You need to get your tank in order before you even THINK about getting more fish. The fish shouldn't just die, there is reasons for the deaths that you are unaware of. First off emerald cory are not good for a 10g. Cories should be kept in schools of at least 3, and 10 gallons is not big enough for 3, they grow over 3 inches. Also with tetras, they need school of at least 5, and there are very few tetras that are suitable for 10g because of there activity level. Furthermore, you should not let guppies just reproduce because you have a friend that will take them, you shouldn't rely on other people to constantly take your guppy fry. If you are interested in guppies just get males. Now for stocking ideas... How about 1 dwarf gourami, 5 Pygmy cories or kuhli loaches, and 2 male guppies. You can keep the 1 emerald in this stock, but you should find a new home for it where it will have more emerald friends and more space to scavenge.