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Problems can occur after water changes under special conditions. However, such individual cases should not be used as an excuse to neglect regular water changes.
Why water changes are necessary
Water changes remove pollutants (e.g. nitrite) that accumulate in the aquarium because they are not completely broken down in the filter.
In addition, regular water changes ensure a balanced nutrient ratio in the aquarium.
With simultaneous and appropriate fertilization, plant growth is stimulated and algae do not become a nuisance.
What affects the water quality
fish
Nitrate, phosphate and other substances are constantly introduced into the aquarium water through the fish food. The amount of substances introduced depends on the amount of feed. In general, the more fish, the more often and more water should be changed.
Plant
The aquarium water is enriched with different nutrients (e.g. iron) through fertilization. The plants consume part of the nutrients dissolved in the water, while they do not or only partly need other nutrients contained in the water. Over time, this creates an imbalance between the various nutrients. Further fertilization increases the imbalance. As a result, plant growth can stagnate over time and instead the growth of algae can be increased. Regular water changes remove some of the excess nutrients from the water.
Light
Depending on the level of illumination, plants grow faster or slower and the more or fewer nutrients are consumed. The ratio of the nutrients to each other shifts correspondingly faster.
temperature
The metabolism of fish, plants and other creatures in the aquarium depends on the temperature. A higher temperature accelerates the metabolism. An increase of 2°C in the aquarium doubles the metabolism. As a result, fish need more food and plants need more nutrients and light. There are major imbalances in nutrients.
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When to change water
Ideally, water is changed exactly when too many pollutants have accumulated or nutrients have become too unbalanced. In practice, however, it is impossible to predict exactly for each aquarium when there is too much or too little of a substance in the aquarium.
The amount of substances consumed is different in each aquarium. Even determining exactly how many nutrients must be present in an aquarium is practically impossible. An aquarium with many plants requires more iron than an aquarium with few plants. In addition, the iron consumption of different plant species is different.
For these reasons, the amount of nitrite, nitrate and phosphate is usually used as an indicator for a water change that is due. The nitrite value is particularly important. Nitrite is toxic to fish and should not be detectable in an established aquarium. As soon as nitrite can be detected in the aquarium, the water must be changed. High nitrate and phosphate levels favor the growth of algae. If the nitrate or phosphate value exceeds a desired upper limit, the water is also changed.
However, in aquariums with strong plant growth and economical feeding, it can also happen that the plants consume more nitrate and phosphate than is produced by the food. The amount of other nutrients does not necessarily depend on the nitrate or phosphate level. So nitrate and phosphate are just a guide.
The values can be monitored with appropriate tests from the pet trade. As a rule, after some time you will find that the values fluctuate in a certain rhythm. Depending on this rhythm, the water is then changed without always having to remeasure the values. With more experience, you can tell when the water needs to be changed based on the growth of plants and algae.
How much water to change
So much water is changed that nitrite is no longer detectable and that the values for nitrate and phosphate are below the specified limit values.
Rule of thumb for water changes
Experience has shown that constant measurements and controls of the water values are not necessary in a well-established aquarium. A weekly water change, changing about 30% of the water, is a good rule of thumb. Apart from aquariums with special requirements, e.g. B. breeding, aquariums can be operated successfully in the long term according to this rule of thumb. Nevertheless, constant observation of fish behavior and plant growth is necessary. In pure plant aquariums z. B. a weekly water change of about 90% may be necessary for the plants to thrive.
How to change water
All you need to change the water is a hose and a bucket or other container. The bucket is placed below the aquarium. One end of the hose is held in the aquarium, the other end over the bucket. The mouth sucks briefly and vigorously on the hose. The water must overcome the highest point of the hose by suction. If you use a transparent or semi-transparent green hose that you can buy from a pet store, you can easily see the flow of water in the hose. At the latest when the water arrives at the end of the hose on the bucket, the end of the hose is held in the bucket. It’s also not a problem if some water gets in your mouth. The fish would not survive in really dirty water that is harmful to humans.
When draining the water, care must be taken that no fish are sucked in with it. If there is a fish near the hose, you close the free end of the bucket with your finger or thumb so that no more water flows out. The fish is carefully scared away with the other end of the hose. As soon as the end of the hose in the bucket is opened again, the water flows again without having to be sucked in again. A piece of curtain or foam also prevents fish from being sucked off. However, there is still a risk that a fish will injure itself if it is pulled too hard against the inlet opening. When the bucket is full, the hose is simply pulled out of the water in the aquarium. The water can now be thrown away or reused, e.g. B. for filter cleaning or for watering flowers.
So that the new water to be filled in does not contain any chlorine, the water is allowed to run into the replacement bucket with a powerful spray jet or the water is left to stand for a few days before it is filled into the aquarium. With copper pipes, let the water run down the drain for a few minutes beforehand and do not use warm water directly from the pipe.
When filling the aquarium, the bucket with water is placed above the aquarium and the procedure is the same as for draining the water. To avoid disturbing the substrate, allow the water to run into a small bowl or cup that stands on the ground or floats in the water. A watering can can also be used instead of a bucket with a hose. If you leave the pouring attachment on the jug, you don’t have to pour the water into a bowl or cup. In this case, a downpour is simulated. The watering can can of course also be used when draining the water. The water can then be poured out more accurately. Of course you can also use several smaller jugs and let the changing water sit in them for a few days to remove chlorine.
If there is a lot of sludge in the aquarium, it can be sucked off at the same time as the water is changed. To do this, the end of the hose is guided over the ground in such a way that the light mulm is sucked off, but the heavier sand or gravel ground remains. Mulm bells can also be used. In a mulm bell, the substrate can rise a bit and then sink back down again.
Some sludge bells have a filter pad as protection against the suction of the substrate. A sludge bell can be carefully placed in the ground to suck up sludge in the ground.
In order to completely avoid dragging buckets or jugs when changing the water, a hose connection with attachable connectors (e.g. Gardena) can be made between the aquarium and the bathtub, shower or washbasin.
Which technique is finally used depends on personal preferences and the size of the aquarium.
Water change and filter cleaning
Changing the water also removes pollutant-degrading bacteria from the aquarium. A large part of the bacteria settled in the filter material is also removed during filter cleaning. It is often recommended not to change the water and clean the filter at the same time, otherwise too many bacteria will be removed and there is a risk that the nitrite level will rise.
However, it’s quicker and easier to do both at the same time once you’ve been working on the aquarium. Since the bacteria quickly multiply and spread again, no problems are to be expected with moderate water changes (approx. 30%) and careful filter cleaning at the same time. However, caution is advised with heavy water changes and very thorough filter cleaning.
Poisoning from water changes
Fish can get used to polluted water if the pollution increases slowly over a longer period of time. Symptoms of poisoning can occur in such fish with a sudden, strong water change with unpolluted water.
Will e.g. If, for example, fish are taken over that come from an aquarium that has not been maintained for a long time, they should be acclimated slowly. Radical water changes should not be carried out in aquariums that have not been maintained for a long time. They should be switched over slowly. The strong water changes, which are rightly recommended in most cases, can cause damage in these rare cases and even lead to the death of the fish by poisoning.
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Deaths after water changes with almost pure osmosis water
Photos: Robert Christman
After a water change with almost pure osmosis water, a white mass or mucus escaped from the shown halfbeaks, Dermogenis pusillus. The animals died within a few minutes immediately after the water change. There was significantly more mucus than could be captured in the pictures.
A few years earlier, halfbeaks had died after changing the water with osmosis water. The exact cause of death is unknown. It may be related to the greatly changed osmotic pressure.
A similar phenomenon occurred with the root shown below after every water change until the root was removed. The emerging white mass was eaten with preference by shrimp.
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