Most active invertebrates such as shrimp, octopus, lobsters, and crabs, prefer a chunk of solid food that they can tear apart with their mouth parts. These animals often feed at night and are adept at finding small food particles that the fish may have lost during the day. A few small pieces of frozen shrimp or fish dropped into the tank after lights are out, will usually keep these animals well fed since they don't have to compete with the fish after dark.
    Good algal growth in the tank keeps most of the slow moving grazers like hermit crabs, nudibranchs and sea urchins happy. If you live near the sea, a rock heavy with marine growth provides much food for invertebrates and some fish. Beware of parasite introduction to your tank. Unless the “live rock" is put through a quarantine, it may be best to restrict it to an “invertebrate only” tank. Many of the invertebrates now kept are basically plankton feeders such as tube worms, some anemones, corals, and bivalve mollusks. They all have some sort of feeding mechanism that catches, traps, or filters out the tiny planktonic organisms that normally surround them. There are two ways to feed these animals with live organisms: introducing the organisms to the tank or removing the invertebrate from the tank to place it in a feeding tank. Newly hatched baby brine shrimp are a very good food because they are nutritious, do not foul the water, are easy to produce, and are readily taken by filter feeders. Wild caught live ocean plankton is also very good, but besides being difficult to get, it may also introduce disease organisms to the aquarium. There are companies that offer plankton food sources for reef tanks, and many have reported good results using them.
    A turkey baster is a handy tool at feeding time. Concentrate the brine shrimp in a cupful or two of saltwater and use the baster to direct a stream of brine shrimp nauplii into the vicinity of the filter feeding invertebrates. Some animals such as small anemones that are attached to a moveable rock, feather duster worms, small basket stars, some soft corals, and barnacles can be removed from the aquarium and placed in a bucket or a feeding tank with a high concentration of new hatched brine shrimp and good aeration. After several hours they will be well fed, and can be replaced back into the aquarium. Feeding this way you have to try and match the tank water parameters as close as possible, you can use some of the tank water to do this with, and then add the water back to the tank to release any leftover food into the aquarium for other animals to eat.

    A marine aquarist can now buy good quality marine foods, from flake food, frozen formulas, marine pellet for bottom feeders, plankton mixes, romaine lettuce or spinach leaves for fish that are mostly herbivores. And this will keep most marine fish, invertebrates and corals happy. Also remember light is a source of food to some animals also do not overextend the changing of lights also as this can cause a loss of a food source due to light output being less and a change in spectrum. As long as the feeding is fairly regular, not too much at the same time, and you include as much variety as possible, your tank's inhabitants will be “happy”.
    An aquarist can also grow or buy marine macroalgae, (Caulerpa, Ulva sp.) for fish, make up a shrimp based food mix with vitamins B and C every month, add a little iodine and minerals to the food mix (from a health food store), and feed live brine shrimp grown out in a green microalgae culture every two or three days, then you will really have happy fish and invertebrates.

These are a few comments and ideas on foods and feeding, most are just common sense, that will help you satisfy the nutritional needs of your aquatic friends.

1. Strive for variety in food sources. Avoid feeding one kind of food item exclusively over a long period of time. Don't use rancid fats and oils, don't feed seafood items that smell decayed.
2. Avoid too much fats, most marine tropical fish should have 10% or less fat in their diet.
3. Avoid foods compounded for freshwater and cold water fish, especially trout and salmon, too much fat.
4. Avoid large amounts of carbohydrates for carnivorous and omnivorous fish. Carbohydrates should be less than 5% of the diet for most marine tropical fish. Most marine fish also do not need much fiber. Usually about 5% or even less, is apparently enough for most marine fish.
5. Feed high protien foods. The diet of most tropical marine fish should be 40 to 60% protien. Feed protien from various marine animal sources to include all the various essential amino acids for all the different species that are in the tank. (Hmm funny let's see 10% fat, 5% carbohydrate, 5% fiber, and 60% protien comes out to 80% ¿?€) Oh yeah the other 20% of the diet, the fish will buy from the black market and make it themselves. These are just rough guidelines, but you should give you some idea of the direction to go with providing food for marine tropical fish. Why do I say marine tropical fish? Well there are marine fish that are not from the tropics, some are from colder waters like the artic.:)
6. Supplement the water soluble vitamins C and the B group, especially C. The oil soluble A, D, E, and K are less important to supplement if a good variety of fresh foods are fed. A little brewers yeast in the food mix is a good source of the B vitamin group.
7. Iodine is often lacking in the diet of marine tropical fish and constant lack of iodine can cause goiter. Supplement iodine if fresh foods are rarely fed.
8. Fish color, especially yellow, orange, and red, is greatly enhanced by the addition of certain pigments to the diet. The most effective pigments are the carotenoids canthaxanthin and astaxanthin. Beta carotene is probably the only caratenoid aquarists can find, and it's slightly better than none, but fish generally cannot use beta carotene effectively. Astaxanthin on the other hand, with proper lighting, will brighten up yellow, red, and orange fish remarkably. Look for foods that list canthaxanthin and astaxanthin in the ingredients. Note that some foods designed to enhance the color in freshwater fish contain the male hormone testosterone. This is ineffective in enhancing the colors of marine fish that are not breeding colors. A good dose of testosterone, however will quickly take the need to breed out of any female of any fish species.
9. Breeding fish require great attention to diet. Find and supply the natural diet for the species that is to be bred, or a good natural (fresh or frozen) substitute.
10. Raw foods of marine origin provide the best mix of essential nutrients, but also carry the greatest risk of disease and parasite introduction. Feed raw marine foods, but be careful, and select the foods only from fresh and healthy sources. Freezing better preserves the nutrition of marine foods than cooking, but it is not as sure a control of disease contamination as in cooking.
11. Use a turkey baster to squirt small particulate foods or small live foods directly at specific invertebrates or in the vicinity of corals and small fish.