It seems that there is nothing complicated about changing the water in an aquarium: drain some of the old water and add fresh water. But it is this simple procedure that is the basis for the health of your underwater world. Incorrect actions can be harmful rather than helpful, causing stress to the fish and disrupting the fragile balance of the environment.
Many novice aquarists think that water should be changed as infrequently as possible so as not to disturb the inhabitants. In fact, regular and competent replacement is like airing a room: it removes accumulated harmful substances that are invisible to the eye and saturates the water with essential elements. This is the most effective prevention of many problems.
Let's figure out how to do it right so that your fish remain active and your plants delight you with their lush greenery. We will talk about how often and how much water to change, how to properly prepare fresh water, and what to pay special attention to during the process.
A little theory: why change the water
Changing the water in an aquarium is not a whim, but a pressing need, which is due to a number of reasons:
- The presence of organic matter in water is accompanied by its chemical transformation—decomposition.. In the first stage of this process, ammonia is formed – a nitrogen compound that, in its pure form and in high concentrations, is dangerous for aquarium inhabitants. Bacteria convert it into nitrites and then into nitrates, which are consumed by plants to reproduce the nitrogen cycle. Over time, the nitrate level exceeds the plants' ability to absorb it, leading to poisoning of the environment.
- Natural contamination over time. Like any biotope inhabited by living organisms, an aquarium gradually becomes polluted by the waste products of its inhabitants: plants produce dead and decaying fragments of stems and leaves, fish, mollusks, and crustaceans shed their scales and excrete waste into the water. In addition, food residues that are not eaten by the inhabitants accumulate at the bottom.
- The aquarium biotope tends to shift the acid-alkaline balance towards a decrease in pH. For many tropical fish and plants, a slightly acidic environment is optimal for development, especially since the minerals dissolved in the water neutralize the acids. Over time, the amount of these substances decreases, and further increases in water acidity can exceed the limits that are comfortable for the inhabitants.
- An imbalance in the water leads to a decrease in the immunity of fish., even if they adapt to the existing conditions. This leads to morbidity, as the development of undesirable bacteria and harmful fungi is observed in parallel.
Considering that nitrogen, minerals, and acidity levels are necessary for normal plant life, aquarists should select a suitable water change schedule based on the needs of the fish, shrimp, and aquatic plants living in the aquarium.
To keep aquarium inhabitants feeling good, the water needs to be changed regularly — about once a week, replacing about 20-30% of the volume. This helps remove harmful substances such as ammonia and nitrates and maintain cleanliness without stressing the fish. The main thing is not to change all the water at once and to use settled or filtered tap water that is close in temperature to that in the aquarium. This will preserve beneficial bacteria and not harm the fish.
Complete and partial water changes
Any aquarium may occasionally require a complete water change. This is a serious undertaking, leading to a complete change in the biotope — no wonder experienced owners call it a restart.
This is very stressful for fish, so there must be compelling reasons for a complete water change:
- an infectious disease has been detected in the aquarium.
- the tank has been attacked by fungus or there has been a severe algae bloom, and no other remedies are helping;
- there is a mass death of fish or shrimp.
- silting has reached a critical level, so siphoning the soil is clearly insufficient.
If there are no serious signs indicating the need for a complete replacement, the aquarium can go for years without a complete replacement. In this case, periodic partial replacements play a key role.
The main rules for proper water replacement
There are general principles that most aquarists follow when changing water. They are universal and aimed at bringing maximum benefit:
No more than 25% of the total volume should be replaced.. A larger amount of water will be perceived by the fish as a noticeable change in balance, which can lead to stress and disease.- Water must be prepared in a certain way. For most regions, ordinary cold tap water, previously settled or purified in some other way, is suitable. If the water is extremely hard, it must be mixed with filtered or distilled water to reduce the hardness.
- The temperature of the water supplied to the aquarium should be the same as the main body of water.. This will help avoid discomfort for the inhabitants, especially capricious fish native to South America, which react sharply to changes in parameters even by a couple of degrees.
Water purified using ion exchange and silver-containing filters should not be poured into the aquarium. The best option is reverse osmosis purification. Such water is completely neutral and contains no impurities. However, it should not be poured in its pure form either, as this will result in a lack of salts and reduced hardness, which is bad for plants. It is best to mix it in the right proportions with tap water, measuring the hardness (Gh) of the latter.
— Arend van den Nieuwenhuizen Aquascaper
How to determine the amount and frequency of water changes
Both parameters depend to a large extent on the quantity and quality of the living creatures inhabiting the “tank.” Thus, in an aquarium with a large number of fish, prone to overpopulation, the water is changed more often than in a sparsely populated one. A significant number of plants balances the volume of biological waste from the animal world, involving them in the nitrogen cycle. However, this does not mean that a planted aquarium can be left without water changes at all.
Much depends on the age of the biotope formed behind the glass in the aquatic environment:
- In a new aquarium water changes are not required for 3 or more months, as this is when the ecosystem is established.
- Young aquarium (up to 1 year old) rarely requires more frequent replacement than once a month, and the amount can be 10% of the total volume.
- In a mature aquarium, which was started a year or two ago, replacement is required about twice a month.
- An old aquarium, in which the ecosystem is fully formed and established, replacements are made frequently, but in small portions – about 15-20%, but every week.
The frequency of water changes depends heavily on the volume of the aquarium. The more water in the tank, the greater its inertia, which means that the accumulation of harmful substances is slower. So, for a 20-30 liter aquarium, water changes should be done at least once a week, a 50-100 liter tank will require this procedure half as often, and for a 200 liter aquarium, once a month will be enough, provided that the maximum water change volume is 25% of the total.
About water preparation
For most owners, the source of new water is the tap water system that supplies drinking water.
Freshly drawn from the tap, it is not suitable for refilling for a number of reasons:
- High chlorine concentration. Chlorination of water kills germs, but it is equally harmful to fish, snails, and shrimp. Chlorine evaporates, so the danger of poisoning can be avoided during the settling process.
- Water saturation with gas bubbles. Most often, it is ordinary atmospheric air that is present in water in the form of tiny bubbles. You can verify this by pouring water into a container and leaving it for several hours: the walls of the vessel will be covered with numerous bubbles. During settling, the bubbles stick together, increase in size, and burst, rising to the surface.
Excessive saturation of water with air bubbles can lead to gas embolism in fish—the body becomes covered with small bubbles, the fish behaves restlessly, falls on its side, and its gill covers are closed. Bubbles can clog blood vessels, which is certain death. Therefore, it is simply necessary to let the water settle. The settling time varies from two days to two weeks.
Life hack
If the container is small, it is not difficult to settle 20-30 liters of water. But owners of 200-300 liter aquariums have a harder time. In this case, when completely replacing the water, tap water is poured directly into the aquarium and left for several days. Plastic containers in the form of horizontal and vertical barrels are well suited for periodic partial replacement. If the aquarium is very large, it is worth purchasing a small submersible pump with a polymer hose.
Other methods of preparation include boiling and freezing, but due to the labor intensity of these processes for large amounts of water, they are rarely used.
Sequence of work
Even partial water replacement is a whole set of measures that are carried out as necessary. They have their own order, determined by the logic of different actions:
- Cleaning the filter. This is done first. It mostly applies to internal filters, since external ones can be cleaned by simply temporarily shutting off the water supply.
- Cleaning the walls from scale and fouling. This is done with special brushes and scrapers. If necessary, you can also clean grottoes and other objects from growths.
- Working with plants. At this stage, reduce the volume of accumulated green mass (if necessary), remove dead shoots, and thin out the plants.
- Cleaning the substrate with a siphon. Using a purchased or homemade siphon, pump out some of the water from the bottom area along with the silt and organic debris. Sometimes during this operation, the necessary 15-25% of water is removed.
- If this does not happen, use a tube covered with a net to suck water from the middle or surface layers.
- Add water using a pump or the “old-fashioned” way place the container with settled water higher and pull the air out of the free end. Make sure that the jet is not too powerful and does not hit the fish.
Q&A
How can I reduce the frequency of water changes?
Cover the aquarium with glass, do not overpopulate it with inhabitants, and do not overfeed them.
Are there any special products for improving tap water?
Yes, you can buy conditioners that improve the quality of tap water at pet stores and online. However, their use does not eliminate the need for settling.
Is it permissible to use filtered water?
Only water that has passed through carbon filters. Other types of filtration enrich the water with substances that can be harmful to fish.
How can I achieve the desired temperature before changing the water?
During the settling process, the water will reach the desired temperature within a couple of days. If warmer water is needed, it is heated using a low-power electric spiral heater, stirring constantly.
Is it necessary to remove the fish before changing the water?
If the aquarium is small, it is better to move the fish to a holding tank. In large tanks, this is not necessary for partial water changes; you only need to cover the siphon tube with a mesh.
Changing the water is not that difficult if you approach it wisely and do everything correctly. Over time, it becomes a habit and a kind of ritual.
Regular and proper water changes are the key to a beautiful and healthy aquarium. This is not just cleaning, but an important procedure that maintains the natural balance in your little underwater world.
Remember this simple rule: it is better to change the water little by little, but more often. A sudden replacement of a large volume of water is very stressful for fish and beneficial bacteria. Small, weekly changes will help you consistently remove harmful substances without disrupting the established ecosystem.
Always let tap water stand for a while to allow the chlorine to evaporate. And make sure that the temperature of the fresh water matches the temperature in the aquarium as closely as possible. That way, your pets won't even notice the change.
In the end, your efforts will pay off handsomely. Clean, clear water, bright and active fish, lush plants — that's what you'll get by spending a little time on this simple ritual. It's the surest path to success in aquarium keeping.
