When it comes to setting up a successful freshwater aquarium the thing you need most can't be bought – that's patience. Your fish will be depending upon you to provide a stable, well-balanced little ecosystem for them and that won't happen overnight no matter how much equipment you buy or how much you spend on it. The time you set up your tank until the time it's ready for a school of fish will be a matter of weeks, not days. Shortcutting this process will most likely mean you will spend more time trying to correct the conditions in your tank than you will enjoying it.
Step One: Location
Set up your tank in a room and in a place in the room where the temperature remains fairly constant. This means away from a window, away from a radiator or heating duct and even away from a south-facing wall of the house.
Make sure you have electrical outlets nearby or one within reach of a surge protecting extension box. Using a surge protector of the kind used for computers will protect your equipment from shorting out if there is an power surge. If water drops on it, the surge protector will cut off without causing a short circuit in your pump or heater.
Step Two: Wiring
Run the wires of the heater, pump, and filter behind the tank, tie them together with a twist tie and ideally tie them to the tank stand. When you're working on the tank, loose wires will get in the way and may cause you to trip on one and pull it out.
Step Three: Heaters, Filters and Pumps
Your power filter will hang on the back of the tank, its tubes inside the tank. Your heater will connect to the tank edge and hang inside as well. An under gravel filter will be set into the tank and the tubing will need to be connected as the instructions direct. Your air pump should be set on a solid surface outside the tank so its vibrations will be minimized. You will have to set an aerator inside the tank and run the tubing to the air pump. Most tank covers have cutouts provided for the filter and thermometer. Do not turn anything on until you've got water in the tank.
Step Four: Gravel, Rock or Sand
Wash your gravel, sand or rock thoroughly and then put it into the tank. It should not be more than an inch deep if that. Too deep and food and detritus will sink into it where it will rot. Arrange rocks to provide hiding spaces for the fish.
Step Five: The Water
Now you can add water. Add it slowly to prevent the gravel from shifting too much. When you've got the tank about half-full, reach in and spread out any gravel that's been moved and do a final arrangement on the rocks and shelters. If you are adding plants, either live or plastic, now is the time. Anchor them well into gravel. You can purchase plant anchors in a pet or aquarium shop. Now slowly add the rest of the water and turn on your pump, heater, and power filter. You may have to pour a little water into the power filter to get it started.
Now comes the first period of waiting. Add de-chlorinating liquid in the proportions recommended on the label. Set your heater and over the next day or two, check the temperature readings at various times of the day until you've stabilized the water temperature. Now test the pH and nitrate content of your water. Hang a notebook on the side of the tank and write down these levels.
Step Six: Biological Filtration
The next step is to start the process of biological filtration. This means developing colonies of nitrifying bacteria in the tank to levels high enough to counteract the increase in nitrates from fish waste. To do this, buy a couple of inexpensive fish, perhaps a couple of corydoras cats and a couple of barbs and introduce them into the tank being careful to acclimate them to the temperature of the water first, and getting as little of the fish store's water into the tank as possible.
Over the next several days, take nitrate readings in the tank. What will happen is that the fish waste will at first make nitrate levels jump. Then, as the nitrifying bacteria begin to break down the nitrates, the levels will drop off. You want your nitrate readings to get back to zero. This process may take a few weeks. If the nitrate readings go up during that time and don't drop off in a few days, make a partial water change. Here is where your patience will pay off. The establishment of good bacterial colonies is key to a trouble-free tank and stress-free fish.
Step Seven: Deciding on Fish
During this time, decide what other fish you will want. Study the fish stores for those with the best stock. And read up on the needs of the fish you choose. Once the tank is ready, add your first fish or group of fish. Nitrate levels will increase once more but should come down quickly. Do not add more fish until the nitrates level off. Again, a few week's wait will make certain you haven't introduced any diseases or parasites into the tank and will keep you from ending up with more sick fish.
Step Eight: Patience
The key is patience.