Aquarium fish need clean water to thrive. However, what is clean water?  People may have different definitions. Many people assume if the fish tank water looks clean without any funny smell, then the water quality is excellent.  It is true that color and smell of the aquarium water are both important indicators of water quality.  They are not the only aspects that matter.  Nor they are the most important.

A poorly maintained aquarium might have cloudy water and odor, but it might also have crystal clear water without any odor. Some of the most common potential harmful chemicals in an aquarium have no color or smell, e.g., ammonia, nitrite, nitrate, and phosphate, just to name a few.

Ammonia and nitrite are both toxic to fish, and we must keep both at 0ppm all the time to avoid damage to fish. Nitrate and phosphate, on the other hand, are relatively harmless, but too much of them can also affect the water quality in an aquarium. High concentration of nitrite can weaken fish immune system in the long run. Combined with too much phosphate, nitrite can also cause an algae boom in an aquarium.

Excellent aquarium water quality must be crystal clear with no odor. It must be free of toxic such as ammonia and nitrite. Low on organic waste such as nitrate and phosphate and low on harmful bacteria population. And it must have decent water buffer, thus stable water hardness and PH.

How to Keep Aquarium Water Clean in an Aquarium?

1. Do not get a fish tank that is too small.

When you have a small fish tank, the water quality can be highly unstable. The more water, the easier it is to keep the water clean. Getting a good-size fish tank is the first step for proper fish keeping. In fact, it is recommended you should get the biggest fish tank your budget and room space allow.

2. Get a high-quality aquarium filter system.

With a highly efficient aquarium filter system, an aquarium is easier to keep clean. The most important function of an aquarium filter is the biological filtration. To make sure there is enough filtration, you need to check the manufacturer recommended tank size on the filter. They usually have the description of “up to 20-gallon”, “up to 40-gallon” type rating. Get a filter that is rated higher than the size of your fish tank will provide good filtration. Keep in mind; you can hardly get too much filtration. It is the more, the better unless the filter produces current that is too strong for the fish.

3. Fishless cycling the aquarium before getting fish.

Before you get fish, you need to do a fishless cycling to your aquarium after everything is set up and running. Fishless cycling can get the aquarium nitrogen cycle going in a newly set-up fish tank to avoid so-called “New Tank Syndrome.” It is the only way to keep the toxic ammonia and nitrite at constant 0ppm. Tetra SafeStart is a great product to give a jump start to the aquarium nitrogen cycle by heavily seeding the beneficial bacteria in the filter media.

4. Use a good aquarium water conditioner

Some of the water conditioners such as SeaChem Prime can temporarily detoxify ammonia and nitrite. It is highly useful for a newly established aquarium or any aquarium keeper who worries about potential ammonia and nitrite spike.

5. Do not overstock your fish tank.

When you have too many fish for the size of your fish tank, it is next to impossible to keep the water clean. Save yourself some trouble by having the proper number of fish according to the size of your aquarium. It is always easier to maintain a lightly stocked aquarium.

6. Use high-quality fish food.

It is understandable that high-quality fish food will keep the fish healthier through the higher nutrition value. High-quality fish food can also keep the aquarium water cleaner. A lot of low-quality fish food contains a lot of useless fillers such as wheat flour, which can break apart easily or even partially turn into fine dust while fish are eating them. It can directly result in more leftover fish food after every feeding. Fish also can’t digest all the filler. Therefore, more fish poop is produced when the fish are fed with low-quality fish foods. Using high-quality fish food can reduce water pollution by reducing both leftover fish food and fish poop.

7. Do not overfeed your fish

Overfeeding contributes many problems in aquarium fish keeping. It includes water pollution in the form of ammonia and nitrite spike, as well as cloudy and smelly water. Overfeeding will directly pollute the water in a fish tank through the rotting leftover fish food. Even when the fish ate all the extra fish food, they will produce more poop than if they have eaten less. Both the uneaten fish food and additional fish poop will produce ammonia, nitrite, nitrate, as well as phosphate. Feeding the fish lightly is the key to keep your aquarium water quality high by reducing the source of pollution. For more information on how much to feed your fish, please refer to
How Often and How Much to Feed the Fish.

8. Weekly aquarium maintenance

Regular 30 to 50% partial water change on a weekly basis is necessary to keep the nitrate and phosphate concentration in check. Removing fish poop and other organic waste by substrate vacuuming should also be done at the same time. Fresh clean water is also needed to restore water buffer to keep the water PH stable. Weekly aquarium maintenance can avoid so-called “Old Tank Syndrome” and help to keep aquarium water quality excellent.

9. Natural supplement/addictive for aquarium water

Some aquarium products such as Immune Plus (or Immune+) from Tropical Science, are designed to provide extra beneficial bacteria that will compete with potentially harmful bacteria by eating up the same food source. These bacteria feed on organic wastes such as fish poop and leftover fish food. By having more good bacteria will keep the harmful bacteria such as Columnaris down. Regular use of such product can reduce fish loss by preventing bacterial and fungal infection.

10. UV lights

If you are willing to spend extra money, getting a UV light for your aquarium can directly kill harmful bacteria and parasites in the water column. Some people also use UV light to kill aquarium algae.

11. Diatom filter

Some experienced fish keepers use diatom filters in addition to their regular biological filtration. Diatom filters can remove small particles down to micro. Diatom can filter out all the microscopic-sized organic waste, algae, even parasites. A fish keeper told me that his aquarium had been disease and parasite free for more than ten years thanks to his diatom filter. If budget is not a concern, then why not?

To keep excellent aquarium water quality, it is more than just to keep the water clean.   However, it is an easy task if you follow the first eight tips. They are mandatory for almost all fish keepers (except for RO water users and saltwater aquarium keepers). The last three tips are for advanced fish keepers who have the extra money to spend, and they are not must but nice to have.