How to set up and keep a 55 gallon fish tank
So you've decided on a huge 55 gallon tank. Here's what you need to think about before you set it up:
Where will you put it? A talk this big will be about four feet long and two feet wide, and will weigh a lot empty-- full of substrate and water, it will be far too heavy to move. You'll need either a stand built for a tank this large, a sturdy bar or half-wall strong enough to hold it, or a big and solid piece of furniture to put it on. Make sure that it's perfectly placed on an even and level floor before you start filling it, because you won't be able to move it after it's set up without taking it all down again.
What fish do you want in it? The kind of fish will determine which plants you put in, what kind of substrate, whether you need a water heater, whether you need water conditioners or additives, what kinds of lights you'll need... the list goes on. If this is your first tank (it's very bold of you to just jump in with such a large one!), it's suggested that you keep something simple like goldfish, which don't much mind temperature or acidity fluctuations, or guppies, mollys and platys, which breed easily and keep up their numbers on their own.
If you want to keep a full ecosystem-- fish, bottom-feeders, snails, plants, shrimp, and so on-- you'll have to account for all their needs when you plan out the tank. There will have to be places for each to hide where the others can't get it, there will have to be an appropriate number of each (a rough rule of thumb is an inch of fish for each gallon of water-- and any creature counts as a fish in this matter) to avoid overcrowding and violence, and all will have to be able to get food.
The number of fish will also determine what kind of filtration you need: lots of fish will make lots of waste that will need to be cleaned out of the water.
How much time do you have to devote to the tank? Especially in a new tank, it will take a while for the balance to settle in, and so you'll have to deal with sick fish, fluctuating water conditions, sometimes fishy violence, lighting and plants related issues, introducing new animals to the tank... You get the idea. If you don't have a lot of time, you might want to reconsider setting up a small pond in your living room, and maybe opt for a smaller tank instead. If, however, you do have time, then go for it, and design the best tank you can get!
Setting up the tank
A fish tank needs water, filtration, and substrate. After that comes decoration.
Filtration: Filters appropriate for your tank should come in the kit when you buy the tank, but if you aren't buying it new, you might need to get the filters separately. Most pet stores with a fish section will sell filters and all the various materials that go in them, and the box should say how big of a tank they are appropriate for. Big tanks may need two or maybe three filters to stay clean. Set up the filters according to the directions, and set them on the back of the tank with a way to plug in to a reliable power source. A power strip is good for this, because you'll also have to plug in the hood lamps.
Substrate: There are any number of different kinds of substrate, varying from marbles to river rocks, sand to stones to broken coral. The main purpose is for the bacteria who help balance the tank's chemistry to have somewhere to live, and for little creatures like clams and shrimp to have shelter. If you plan to have tunneling creatures, you'll need deeper, smaller-grained substrate; if not, you can go with big stones. Just make sure the substrate in question is small enough or large enough not to get stuck in the mouths of the fish that will be living with it (this is especially true for goldfish and others that will actively dig in the bottom). Additionally, something calcium-based like coral or crushed shells will help counteract the acidity produced in the fish waste, but may make the tank too basic / alkaline; be sure to check the ph balance periodically to be sure it's appropriate. Don't line the tank with anything jagged or sharp; fish can be hurt as easily as any other animal. If it's not new substrate, be sure to wash it well and soak it in bleach water to kill germs that could harm your fish (exception: if you have substrate from a healthy, balanced, functioning tank, throw it into the new tank with the bacteria load as is-- it'll speed up the balancing).
Water: For a tank this big, the only really reasonable option is tap water, unless you're rich enough to buy 55 gallons of spring water to fill it with. A hose helps fill the tank quickly. Tap water, however, is usually full of chlorine, which can be harmful to fish, so be sure to buy a big bottle of water conditioner. It'll counteract the chlorine and make the water safe for your fish.
A few tablespoons of aquarium salt will help keep the bacteria in check; the side of the box will tell you how much.
After everything is together, let the water sit in the tank with the filters on for several days-- it'll help get the chlorine out, and will start the tank producing the bacteria it needs to balance out.
Decoration: You can really decorate your tank any way you see fit. Just be sure there's enough light of the right kind for the plants you want to keep in the tank, and that any décor doesn't have jagged edges that can hurt the fish. Watch out for small spaces a fish could get into but not out of-- a trapped fish can quickly suffocate. Make sure the plants you choose aren't poisonous for the fish you want, and make sure they all have the same light needs. Google them to find out if they need CO2 supplements or if they're too delicate for fish or snails to chew on them (snails, especially, as an overabundance of them can quickly eat up all your plants).
Ebay has a fun selection of decor-- everything from rare plants to strange statuary-- and there are any number of dedicated shops online for all your aquarium needs.
Adding the fish
If this is a brand new tank, add just one or two fish at first, preferably a hardy sort. A freshwater tank can start with some feeder goldfish, usually a quarter or less each, while a saltwater tank can start with a zebrafish. These pioneers will start the fish-waste cycle, jump-start the tank's biology, and help the water balance out. It might get cloudy and awful for a day or two, but as long as your fish are still alive and aren't showing any signs of illness (swelling up, clamping their fins against their bodies, getting covered in white bumps or red streaks, etc), it should balance out.
Once the tank is settled, add a few more fish, remembering the one-inch-per-gallon rule. Don't add all of them at once. Too many fish added together will up the waste dramatically, which will cause an overproduction of bacteria, which will quickly destroy your tank biology. When you add them, let them sit in the bag in the water for a half hour or so-- it'll get the water from the pet store and the tank water to become the same temperature so you don't shock the fish when you add it.
Be sure that the fish you're adding will get along with each other. You don't want an aggressive fish in a tank full of gentle schoolers-- it'll beat them up and probably kill them. You don't want a carnivore in with a bunch of herbivores-- it'll eat them. You don't want one giant fish and lots of small fish-- you'll soon have a fat giant fish and no small fish. You don't want a warm-water tropical in an unheated tank-- winter will kill it as soon as the tank's temperature drops even a little. It's easy to find lists online of fish that can coexist.
Maintaining your tank
Once the balance is reached, a tank will mostly maintain itself. Once in a while, pull out the filters and rinse them in water of a temp similar to the tank-- don't sanitize them, just clear them of debris and ease the over-population of the bacteria there. If you rinse them in a bucket, the resulting brown water is perfect for plants, loaded with the minerals a garden needs.
If you get algae, add a little algae-killer to the water and / or get an animal that will eat it like a snail or a plecostomous. Snails tend to come pregnant, though, and you might wind up with hundreds of snails, and plecos are slow and tend to be inactive during the day. If you can keep the tank out of direct sunlight, the algae should die off on it's own. There are devices you can get to scrape the algae off the glass, and the fish might eat it out of the water, but free-floating algae will just settle and grow somewhere else.
No more than once a month, you can change out ten or twenty percent of the water, but be sure to add more conditioner when you do; most of the time in an airconditioned house, the evaporation will be about as much as you'd want to change, so you just have to top it off rather than changing it, unless it's gotten really acidic.
Periodically check the water's composition with a test kit, or bring a sample to a pet store's fish area for them to test it; make the necessary adjustments to keep it in the ranges recommended for your fish.
A happy tank will start breeding. Look up how to handle it, if you want to keep the babies (for instance: guppies will eat the babies before they have a chance to get big enough to survive, and goldfish require something to lay their eggs in like grass or a breeding mop, and might need a secondary tank for the babies if they're to survive). Frequently, fry need different food than adults, and are too small for the current a filter creates. Also, they'll need places to hide while they're small and edible.
Cats will sometimes try to go fishing, and even if they don't, they're fond of moving water and may drink up gallons in a week. Keep that in mind.
If the substrate gets too clogged with debris, you can get a tank vacuum to clean it out, or can invest in shrimp or bottom-feeders to clean it up, but keep in mind that they'll create waste of their own that will need to be handled.
Chunks of activated charcoal will serve as passive filters-- but make sure it's the kind for fishtanks, usually bamboo charcoal, and not the kind for grills, which will have accellerants that can poison your tank!
Zeolite will counter ammonia, and can be added in small amounts to do so. Large shells will dissolve their calcium into the tank slowly, countering acidity.
Driftwood can offer a nice place for plants and fish alike, but if it starts decaying, it'll only add to your tank-balance problems.