Fish food is sold as dried flakes, freeze-dried cubes, pellets, frozen foods, live foods and do-it-yourself live eggs and cultures you can grow. Do not catch food organisms from the wild (ponds, rivers, etc.) because it is unnecessary and possibly deadly -- pathogens and tiny predators can infect your tank and cause undue harm. Many experienced aquarists use their own recipes involving foods like egg yolk, beef heart, shrimp or even catfood. I advise beginners against this , since it is all too easy to foul the water if used improperly. Another thing to avoid are the slow dissolving time-release vacation feeders--usually some kind of white tablet. They are likely to foul the water and kill your fish while you are away. When on vacation, you can leave the fish hungry for a week, they will be better off than if overfed. If you will be away longer than that, arrange for someone to come by every other day and feed a small amount. In general, when feeding, use only enough food that the fish can finish while you are watching them, about one or two minutes. The worse thing you can do to your tank is to overfeed the fish! This is the cause of most tank problems and fish death, because uneaten food causes ammonia problems, which are deadly. Feed your fish two or three times a day. Many small feedings are better than one large one. When making a dried food purchase, it is important to note if the label says "will not cloud the water." Some foods will, even if used sparingly, and the cloudiness is difficult to control.
All of the available styles of foods are good for your fish; live brine shrimp are nutritious and full of protein (especially good for newborn fish a.k.a. "fry"); the higher quality dried flakes and pellets are specifically designed to fulfill all of a fish's nutritional needs, including vitamins and minerals, and sometimes include natural color enhancers. To keep your fish interested in their food and provide them with balanced nutrition, it is recommended that you buy a few different kinds of food and vary your pet's diet. One caveat: match the food to the fish's species! If your fish is a vegetarian, live shrimp will be worthless. If it is a surface feeder, sinking pellets will go untouched. This is why it is very important to buy food designed especially for that kind of fish. You must also consider what type of food the breeder or petstore has been feeding. Many individual fish get used to a specific food, and have difficulty recognizing something new as edible. For example, if your new betta won't eat, give it a few days to realize their usual food isn't coming. If that doesn't work, try a different brand. If it still won't eat, you may be the proud owner of a fish that was treated well by its breeder and fed live brine shrimp exclusively - you may have to start hatching brine shrimp eggs.
One reason food is designed for specific species of fish is that each fish species feeds in one of four ways: surface feeders watch the top, waiting for insects to fall on the surface - they need food that floats, like flakes, and live food that will stay near the surface just long enough to be eaten (e.g. flightless fruit flies). An example is a gourami or a betta. The second category of fish are the middle feeders. They dart around the mid level of the tank catching what passes by. I assume in the wild they are generally chasing smaller fish. In your tank, they do very well catching brine shrimp and other live foods. Manufacturers make special dried food for this type of fish -- pellets that are slow sinking. Of course, they also eat flake food as it falls. Rasboras and many shoaling (schooling) fish are examples of mid level feeders.
The third category are the bottom feeders. Contrary to popular belief, bottom feeders are not able to thrive on everyone else's leftovers. Catfish in particular are often sold as "Janitors" because they will eat food that makes it past the surface and mid-level feeders. That is a wonderful characteristic, making bottom feeders invaluable to a balanced tank. But if you are relying on leftover food to sit at the bottom waiting for the "janitor" you are courting trouble. First of all, your catfish may not be getting the nutrition it needs. Special sinking wafers are sold especially for them, and are recommended. Secondly, if you are depending on other food falling to the bottom, you are making the cardinal sin of fish keeping -- you are overfeeding and allowing food to accumulate at the bottom of the tank. If the catfish doesn't find it, you will have serious water quality problems, as well as a filthy gravel bed. Catfish find their food by bumping into it -- they feel it with the barbels near their mouth. They can easily miss those leftovers, and certainly won't eat them once they have begun to rot. Treat your bottom feeders with the same respect you treat your other fish -- feed them food designed especially for them, do not feed more than they can eat in a short time, and note any special needs that species may have. Some need to be with others of their own kind, but pet store employees don't know this and are happy to sell you one lone fish; then they will tell you it will clean the gunk off the bottom. They don't know what they're talking about. Again, know your species before you buy -- DO NOT RELY ON SALES CLERKS to tell you anything about a fish. Learn what you need to know BEFORE you get there.
FILTERS AND STUFF
THE NITROGEN CYCLE
DISEASES AND MEDICATIONS
PLANTS AND ALGAE