Both guppies and the many species of tetra are popular aquarium fish. Many tetras have a lot in common with guppies: they stay small, tolerate novice owners' mistakes and have colorful bodies. Additionally, both tetras and guppies prefer many of the same foods.
Fish flakes are the most common (and easiest) foods for your fish. You should keep them fresh, and replace old flake food after a few months. Also, even though guppies and tetras will eagerly accept flake foods, you should add other types of food to avoid health problems. Make certain that you use flake foods that are formulated for tropical fish.
Freeze-dried foods are a great option for your fish. They have many of the same benefits of live food, but are much more convenient and carry no risk of transmitting diseases. You can feed them to your tetras or guppies as a staple food (instead of flake foods), though they do cost a bit more.
Many pets shops also carry frozen foods. These make a great treat for your guppies and tetras. They cost somewhat more than freeze-dried foods, but are slightly more nutritious and even more eagerly accepted. You should avoid feeding a single variety of frozen foods; it's never a good idea to feed only a single food, even if it's a higher-quality food.
Live and Fresh Foods
You can also purchase live foods like tubifex worms. Guppies and tetras will eagerly accept any live food they can fit in their mouths. The only catch is that live foods can occasionally transmit dangerous diseases and pests like hydras. Brine shrimp are almost always safe (they are hatched from dry, disease-free eggs) and are a favorite of guppies and tetras. Guppies may also benefit from the occasional feedings of vegetables like boiled zuchinni.