Regular maintenance for any size aquarium should run as follows

Once each week 25% water exchange. This means we need to REMOVE 25% and replace it with clean water.

Do NOT just top off the tank. As stated before, the pollution or "remaining waste" in the water does not evaporate, therefore if you you top off your tank without removing more of the water, you can and will make the pollution problem worse.

Water Conditioner will be discussed in another article and linked here when it's complete. Be careful when doing water exchanges to only treat the amount of water exchanged, not the entire tank repeatedly. This can greatly alter your water quality and harm your fish, and is difficult to resolve.

Once each month a gravel vac is needed to remove the dirt and particles that fall to the bottom and create harmful ammonia. If the gravel is not kept clean, the ammonia levels in the tank rise faster than the bacteria can break them down, and cause lethal conditions for the tank's inhabitants.

Once each month the carbon also must be changed. If an undergravel filter is being used, this carbon must also be replaced. If a hang on filter is being used, the carbon can be found in the form of a pouch, a pad, or a filter bag with carbon inside.

I recommend the purchase of test kits to monitor your own water quality. When something just "doesn't seem right", usually the first answers will come from water test results. There are a few good places online to go for advice, and many local pet stores can lend advice over the phone. This is most easily done if you can read the test results over the phone or post them on a message board.

Fish respond in specific ways when water quality is not maintained properly. Much as your family doctor will perform a string of tests to diagnose a problem, so the water test is but one way for us to determine fish illness, and to catch it early enough to cure it, and possibly prevent it from happening again.

When keeping some of the larger fishes, such as Oscars and piranha, it is most important to monitor water quality closely. When feeding a partial diet of live fish, (feeder fish) we have to be aware that each feeder fish is increasing the load of waste being passed in that aquarium. This is important to take into account when purchasing a filter for your tank, too. Be sure to get a size/model powerful enough to handle the job it will need to do.

Partially eaten feeder fish, unconsumed flake food, pellets, etc will also accumulate over a period of time, but some fish are known as "messy eaters". It is your responsibility as a fish keeper/hobbyist to know if your chosen fish is on this list. As these fish grow, gravel vacs should be performed more frequently until a larger aquarium is possible. If you find floating feeder fish, or parts of them, it is important to remove them from the tank as soon as possible. The bodies will break down quickly, further polluting your water, and raising ammonia levels quickly.

This is now my opportunity to explain what has to be the biggest myth in fish keeping.