Marine fish are a varied bunch. Each species or type has its own method of feeding - some filter feed, drawing in water and siphoning out the food from it, and some scavenge; others prefer to chase their meal or eat only greens; many just don't care what drops in - they'll eat it.
Some species are aggressive eaters, chasing away their tank mates, while others shy away from conflict. Feeding fish, unfortunately, isn't just a matter of dumping a pinch of flakes into the tank. It is important that you know what sort of food to feed your community and make sure that you take care of everybody's dietary needs.
The common problems are feeding too much or too little, usually the latter being the case. Overfeeding poisons the water, so try to observe how much your fish eat and don't throw in too much food at once. You can always add a little more later. However, don't throw in so little food that the dominant fish always wins out.
Many fish prefer live foods. Baby brine shrimp are the best because they are easy to raise on your own. While these crustaceans are young, the so-called nauplii, they are high in fats and good to feed to young fish. When the shrimp become older, they will be high in protein, necessary for juvenile and adult fish - as long as you've cultured them with some vitamins.
You can also use baby freshwater fish such as young guppies, called "fry," to feed your marine species. Keep in mind that freshwater fish will not last very long in the salt water, which makes judging the correct amount to put in your aquarium a little tricky. Mysis shrimp are also very nutritious, but hard to come by, although some better stores sell them. In the summer months, you can toss in any mosquito and gnat larvae you may find. Tubifex and white worms are commonly fed as live food, but these will burrow into the substrate, die and pollute the tank so be wary when you use them. Live foods alone are not enough to keep your fish healthy.
Frozen or Raw Meats
Lean white fish meat and meat from shellfish are among the favorite foods of many marine species. They also help vary your pets' diets so they won't be bored with the same food - after all, they have a varied diet in nature. On occasion, feed them some liver sliced into tiny chunks, lean beef, beef heart scrapings or any such raw unprepared meat. Not only will your fish appreciate it; it will provide them with vitamins and minerals that the live food cannot. If you are going to feed your fish frozen food, be sure it is 100 percent thawed before you throw it in the tank. Crushed snails from the garden or a freshwater aquarium will also serve nicely.
Eat Those Greens
Many fish rely on grazing for a meal. They'll scuttle around on the bottom or along a reef looking for that certain algae. Some fish require it. If you can sustain a healthy growth of algae in your tank, then you are probably satisfying the needs of your grazers, but some fish do require a huge amount. You can supplement that need by throwing some scalded lettuce or spinach in the tank (you scald it - pour boiling water over it - to make it a little softer and less buoyant). You can also throw pre-soaked rolled oats in the tank.
Manufactured foods, of course, are the most convenient and some are very good. They are prepared from various ingredients then pressed into flakes or pellets, or freeze-dried. Freeze-dried natural foods include plankton, krill, daphnia, tubifex worms and bloodworms. However, a diet consisting of manufactured foods alone is inadequate.
The trick with dried foods is storing them properly; otherwise they lose their nutrients. Keep them dry and tightly closed and away from light and heat, preferably in the refrigerator. You should use them within four to six months after you buy them. Flake food alone will not suffice for marine fish. Pellet foods come in two types: floating or sinking. Sinking pellets are good for invertebrate scavengers such as hermits or shrimp. These will sink, swell and food particles will float away, making them useful for filter feeders too. Be aware that leftover pellets can foul the tank, so remove any leftovers.
Remember to stay away from the floating variety of foods (such as floating pellets) because most marine fish are not surface feeders. You can purchase feeders that will distribute the various foods, although some overload the aquarium with food. Make sure, should you decide on a feeder, that it does not end up destroying your water quality. Always remove uneaten food immediately.