If you've had the patience and taken the time to set up your aquarium properly, maintenance should be easy: a matter of not overfeeding your fish; keeping an eye on their health and growth; maintaining filtration, even temperature and water quality; and making regular water changes of at least 25 percent of the tank's capacity.
The best way to keep track of all of this is to keep a simple journal. If all goes well your entries will be pretty dull. But it will also quickly clue you in to anything that goes awry. Here are the basic things you want to note:
Overall Tank Appearance
Is the water clear or slightly cloudy? Does it show any signs of algae growth, either giving the water or the glass a greenish tint? Does food or waste appear to be accumulating anywhere in the tank?
Are your fish active and swimming normally? Are any fighting? Do any fins looked frayed from fighting or nipping? Do their bellies seem full and not sunken? Has one fish suddenly begun to hide out? Do all seem to get their share of the food? Do any come to the surface more than usual? Do their colors seem good? Are they free of spots or cottony growths?
For most tropical freshwater fish, a temperature between 74 and 78 degrees Fahrenheit is fine. More important than a couple of degrees either way, however, is keeping the temperature from fluctuating too wildly. In the first weeks, it's important to record the tank's temperature at different times during the day and at night. If your tank is in a sun-filled room or near a radiator, the water temperature can be affected by several degrees, especially in a small tank. Account for lowering your thermostat at night as well as if you turn on air-conditioning in the summer. Thermometers have a tendency to lose their accuracy. Always have a spare to compare temperature with. Also, for most tank heaters, very little movement of the thermostat can create a big temperature change. Make your heat adjustments in very small increments.
This is the heart as well as the kidneys of your little ecosystem so take good care of it. Make sure the tubes are not clogged with gravel and that the water level in the tank is high enough to maintain a steady flow. Make regular changes of filter material. In most cases this is just a matter of taking out one prepared bag of material and exchanging it for a clean one. Make these changes at least once a week. If you find the filter material becoming fouled after only a couple of days you either have too many fish creating too much waste, or are feeding your fish too much.
When you set up your tank you were looking for a medium pH and a nitrate reading of zero. These readings, taken with testing kits that can be purchased at any aquarium shop, should be taken at least once a week before you make your weekly water change. If your nitrate level rises, it means your biological filtration is out of kilter, which usually means either you have too many fish or you're feeding them too much. A higher level of pH can also indicate the same problems. Make a water change and then test more frequently during the next few days.
Once a week, siphon out a quarter of the water in the tank and replace it with de-chlorinated water of the same temperature as the water in the tank. The best way to do this is to prepare the right amount of water in a clean bucket (one that hasn't ever had soap in it) or in a separate tank the day before. Pour the fresh water slowly into the tank.
Aquarium shops sell many kinds of siphons. When siphoning, run the mouth of the siphon along the gravel at the bottom of the tank to lift out the waste and uneaten food that has settled there. You will be amazed how much waste will come up. If there seems to be a great deal more than you've been able to get in a quarter tank of water, do another cleaning and water change in a couple of days, after your pH and nitrate levels settle back to normal.
While these are the basic maintenance needs, a couple of additional items might be useful.
The Quarantine Tank
Should you notice one of your fish has been injured, or seems ill, remove it immediately to a quarantine tank with the same temperature water to keep an eye on it. This can be a small tank, but it's an important one. If the fish is sick, you can tend to it in the quarantine tank. You may also prevent all your other fish from getting sick.
If you have live plants in your tank, make sure you take off brown or dead leaves before they fall to the tank floor.
Keep a record of when you add fish to your tank. Never add more than a couple at a time and, ideally, keep them in the quarantine tank for a week before you put them in your main tank, for their benefit and for the benefit of your other fish.
Aquarium shelves are full of treatments, from chemicals that kill algae to chemicals that control diseases. Many of these can have unwanted side effects. The best medicine is maintaining good tank conditions.