The 9 Most Important Water Values In A Saltwater Aquarium

water values

The 9 most important water values ​​in a saltwater aquarium contribute to optimal water values ​​in the saltwater aquarium

In addition to functioning aquarium technology, the main success factors for the successful operation of a saltwater aquarium are the water values that determine the composition of the aquarium water.

Below are 9 of the most important water values in a saltwater aquarium:

1. Ammonium / ammonia

Ammonium (NH4 +) is a nitrogen compound that is almost harmless to fish. In saltwater aquariums, nitrogen is mainly brought in via the food and the associated excretions by the fish.

It only becomes problematic when the pH value rises above 7. When that occurs, then ammonium (NH4 +) is transformed into ammonia (NH3), which is toxic for all aquarium inhabitants . Since ammonium (NH4 +) and ammonia (NH3) are in equilibrium with one another, the ammonia value increases the higher the pH value and the temperature.

In salt water aquariums, it is recommended to achieve an ammonia value (NH3) less than 0.05 mg / l . Values ​​above this can usually only be reached during the running-in phase of the aquarium, for example due to the death of sponges and mussels on living stones.

Even ammonia levels of 0.07 mg / l can cause damage to all aquarium inhabitants through Ammonia poisoning.

Water values: Ammoniun in the aquarium

Symptoms of ammonia poisoning in the aquarium include:

  • Apathetic behavior (lying on the floor, swimming sideways
  • Gasping for air near the surface
  • no desire for food
  • sudden deaths
  • strange, strenuous or very hectic swimming movements
  • Red coloration of the gills or reddish banding of the fins

Countermeasures for ammonia poisoning in the aquarium

  • An immediate and larger water change; The fresh water should be adapted to the aquarium water so that the fish do not get an additional shock due to temperature and other water values ​​such as hardness and pH value should be adjusted as possible.
  • Use binding products or other water conditioners that can bind toxins immediately.

Quick summary card for ammonium / ammonia

  • Ammonium enters the aquarium water through fish food
  • Almost harmless ammonium is converted into toxic ammonia from a pH value of 7
  • the higher the pH and temperature, the higher the ammonia content
  • Optimal ammonia value in the marine aquarium: less than 0.05 mg / l
  • Limit value: from 0.07 mg / l all aquarium inhabitants can be harmed
  • if the limit value is exceeded: filtering through zeolite

2. Nitrite

Ammonium / ammonia is converted into the slightly less toxic nitrite (NO2−) by bacteria (Nitrosomonas). This oxidation process is called nitrification.

High levels of nitrite, like ammonia, have a very strong impact on the breathing of the aquarium fish, as it hinders the transport of oxygen in the blood.

In the saltwater aquarium the nitrite value should be below 0.01 mg / l. In the case of nitrite values ​​of 0.1 mg / l or more, it is strongly advisable to change part of the water and to reduce feeding.

Water values: Nitrite in the Aquarium

In saltwater aquariums, it usually comes, except in the run-in period to no increase in nitrite value. This is because that at the time of the peak nitrite (sketch) bacteria do not have enough are present, the nitrite (NO2-) in the for aquarium fish non-toxic nitrate (NO3-) transform.

The nitrite peak takes place in the run-in phase of the saltwater aquarium between the 7th and 14th day.

One of the few possibilities that there can be a significant increase in the nitrite value in a run-in marine water aquarium is that significantly too much food has been added to the aquarium or the bacteria necessary for the conversion of nitrite (NO2−) into nitrate (NO3-) have been killed by a previous use of medication.

Water values in the aquarium

Quick summary card for nitrite

  • Ammonium / ammonia converted by bacteria (including nitrosomas) into the somewhat less toxic nitrite (nitrification) (NO2−)
  • the nitrite value in the seawater aquarium should be below 0.01 mg / l
  • with nitrite values ​​from 0.1 mg / l, change the water partially and reduce the feeding
  • Nitrite peak occurs in the run-in phase of the saltwater aquarium between the 7th and 14th day
  • increased nitrite levels in the run-in seawater aquarium: too high feed intake? Was a drug used?

3. Nitrate

Nitrite (NO2−), which is toxic for fish, is converted into non-toxic nitrate (NO3-) by bacteria of the genus Nitrobacter. This conversion represents the second stage of the nitrification action. Although nitrate is non-toxic for fish, the nitrate value in the saltwater aquarium should not exceed 5 mg / l.

The reason for this is that nitrate serves as a nutritional basis for algae and is often the main cause of uncontrolled algae growth in addition to high phosphate levels. Another point is that with high nitrate levels the growth of small polyp stony corals (SPS) is strongly slowed and the color intensity decreases. For these reasons, pure SPS pools are often operated with a nitrate value below 2 mg / l.

  • For saltwater aquariums with a mixed coral population (soft corals, large and small polyp stony corals, a recommended nitrate value of approx. 5 mg / l.
  • During the running-in phase of the aquarium, the death of sponges, mussels, etc. on living stones can lead to a brief increase in nitrate levels.
Water values: Nitrates in the Aquarium

Cause of high nitrate levels in the aquarium

  • too many fish stocks • too much fish
  • feed added
  • too few / too few partial water changes
  • too weak filter performance
  • too little protein – skimmer performance
  • nitrate-contaminated tap water

How to regulate nitrate levels in the aquarium

In the event that the nitrate value exceeds the target value of 5 mg / l, the following options are available for correction:

If the fish stock is too high / too much fish food is added:

Ideally, the fish stock should be reduced so that the associated daily amount of feed or fish excrement is reduced. If a reduction in the fish population is not desired or possible, the nitrate value can be compensated for by regular (once a week) larger partial water changes (15 – 20% of the total volume).

It should be noted that live rock has a buffer effect for nitrate. This means that the amount of nitrate that was withdrawn through the water change is released back into the aquarium water through the live rock. For this reason there can be a significant, measurable delay in reducing nitrate levels.

Another possibility to reduce the nitrate content if the fish stock is too high is to replace the aquarium technology (filter system and / or protein skimmer) with more powerful devices.

In principle, the daily amount of feed should be checked to determine whether the amount administered is really necessary. Often the mistake lies in the addition of food, that the entire amount of food is put into the aquarium at once and a large part of it is not eaten by the current or the drainage shaft.

For this reason, it is advisable to divide the fish feed into several smaller portions one after the other and to switch off the current while feeding. When feeding frozen food, it should be rinsed under running tap water for at least one minute before use.

Too weak filter or protein skimmer performance:

If filter systems and / or protein skimmers that are too small are the reason for an uncontrolled rise in nitrate, these systems must be replaced with more powerful ones.

Too weak or wrong current:

In aquariums where the current is too weak or the arrangement of the current pumps is incorrect, low- current (dead) zones arise in which sludge and food residues collect. These accumulations permanently lead to a noticeable increase in the nitrate value.

Too little / too little partial water change:

Too few or too few partial water changes are one of the most common reasons for nitrate problems in practice. Over the years it has been shown that with an average fish stocking, a partial water change interval of 14 days with a volume of 10-15% is the ideal way to keep the nitrate level in the optimal range.

Nitrate contaminated tap water:

Often, however, the tap water available is not suitable for direct use in seawater aquariums, because it has too high a nitrate content (over 5 mg / l, often in rural regions). In order to avoid the resulting problems in advance, the tap water can be treated with a reverse osmosis system.

Nitrate filter (denitrification filter):

In addition to the options mentioned above, the aquarium market offers special nitrate filters (denitrification filters). A detailed description of nitrate filters can be found shortly in the second part.

Quick summary card for nitrates

  • Nitrite is converted into non-toxic nitrate by bacteria (Nitrobacter) (nitrification stage II)
  • the nitrate value should be below 5 mg / l in the saltwater aquarium
  • Use of powerful filters and protein skimmers
  • Sufficient flow> Avoidance of low-flow (dead) zones
  • if 5 mg / l is exceeded> search for and eliminate the cause
  • adapted fish stock
  • 14-day partial water change (10-15%)
  • Rinse frozen food with tap water for at least one minute before use
  • Check the nitrate content in the tap water> possibly use a reverse osmosis system

4. pH value

One of the values ​​that is found most frequently outside of the aquarium hobby is the pH value. 

Water values: pH

What is the pH value?

  • The pH value is derived from the ratio of the H + and OH – ions in the water. Ions are generally particles with an electrical charge. Distilled water without air contact contains exactly the same number of H + and OH – ions. This balanced ratio corresponds to a neutral pH value of 7.
  • If the number of H + ions increases, for example due to the addition of an acid, the pH value falls into the acidic range.
  • If the number of H + ions decreases or the number of OH – ions increases, the pH value shifts to the alkaline (basic) range.
  • The pH value scale ranges from 0 (strongly acidic) to 14 (strongly alkaline).

The pH value in the aquarium depends largely on the carbonate hardness of the water. The carbonate hardness in turn depends on the content of hydrogen carbonate ions (HCO3-) in the water. Water with higher carbonate hardness usually has a higher pH value than “soft” water with lower carbonate hardness.  

What is the significance of the pH value for the aquarium water?

The pH value has, among other things, an influence on the gill function and the protective mucous membrane of aquarium fish. A pH value that deviates too much from the optimum can hinder your fish’s breathing

Which pH value is optimal for aquarium fish?

There is no optimal pH value for all aquarium or garden pond fish. Rather, the optimal pH value of the fish depends in part on the origin or the original habitat of the fish.

How can the pH value in the aquarium be lowered and raised?

If the pH value of your aquarium is not in the optimal range, you can influence it by various measures:

How to lower the pH value in the aquarium:

The pH value can be lowered, for example, by means of bog roots, alder cones and filtering over peat. The specialist trade also offers special peat extracts to lower the pH value.

Furthermore, the pH value can be reduced by increasing the CO2 content in the water. CO2 can be added to the aquarium water through CO2 diffusers. Because the pH value is dependent on the carbonate hardness, it is much easier to lower the pH value if the carbonate hardness is low.

How to increase the pH value in the aquarium:

Limestone or marble gravel and the expulsion of excess CO 2 through increased water circulation are suitable measures for increasing the pH value in the aquarium. Please note, however, that a sufficiently high CO2 content is important for the growth of aquatic plants.

5. Total hardness (GH)

The total hardness (GH) indicates the content of dissolved salts in the water.

What is the total hardness?

  • The total hardness (GH for short) is the sum of the positively charged alkaline earth ions dissolved in the water. Calcium, magnesium, barium and strontium are counted among the alkaline earths.
  • The total hardness is essentially influenced by the content of positively charged calcium and magnesium ions (Ca2 + and Mg2 +), as these usually make up by far the largest proportion. This is why calcium and magnesium are also known as hardness builders.
  • The carbonate hardness, on the other hand, is based on the content of negatively charged hydrogen carbonate ions (HCO3-) dissolved in the water.
Water values: Total hardness

6. Carbonate hardness (KH)

What is the carbonate hardness (KH)?

The carbonate hardness, often simply abbreviated as KH, is a unit for the amount of hydrogen carbonate ions (HCO3-) dissolved in water. Hydrogen carbonates are salts of carbonic acid. Calcium hydrogen carbonate and magnesium hydrogen carbonate are usually of particular importance for aquarium water. Ions are particles with an electrical charge. In the case of hydrogen carbonate ions, these are negatively charged ions, which are referred to as anions.

What is the significance of the carbonate hardness for the aquarium?

Sufficiently high carbonate hardness is of decisive importance, among other things, for the stability of the pH value in the water of the aquarium. The hydrogen carbonates serve as a buffer “against” acids and alkalis, which can drive the pH value into the acidic or alkaline range. The higher the KH value of the aquarium, the more stable and tends to be higher the pH value of the water.

What is the interaction between carbonate hardness and CO2?

While hydrogen carbonate ions have an alkaline effect and thus increase the pH value, it is lowered by carbon dioxide. The content of free carbon dioxide (H2CO3) in the water is in turn partly dependent on the content of C02 in the water, as part of the CO 2 dissolved in the water reacts with it to form carbonic acid. The carbonate hardness can thus to a certain extent be viewed as an “opponent” of carbonic acid.

How is the carbonate hardness in the aquarium influenced?

How to lower carbonate hardness

If there is a shortage of CO2 in the water of the aquarium , the plants gain the CO2 they needthrough a chemical reaction from hydrogen carbonate. During this reaction, lime is deposited on the leaf surface of the plant. In the literature there are also indications that special UV-C lamps partially reduce the carbonate hardness. Furthermore, water changes that are too seldom can reduce the KH value in the aquarium. In garden ponds, the higher the proportion of rainwater in the pond, the more the carbonate hardness decreases.

How to increase carbonate hardness

An increase in carbonate hardness is caused, for example, by calcareous stones and marble gravel. These materials are therefore well suited to raising the KH value.

7. Carbon dioxide (CO2)

Carbon dioxide – or CO 2 – is the most important nutrient of all plants.

How is CO 2 measured in the aquarium?

  • CO 2 is created naturally in the aquarium through the metabolism of the aquarium inhabitants. Bacteria, fish and other aquatic life excrete carbon dioxide. Aquatic plants also produce CO 2 – but mainly when the aquarium lighting is switched off. If you have filled your aquarium with a relatively large number of fish and few plants, the CO 2 value should actually be in the green area. But you better play it safe and measure the carbon dioxide content of your aquarium water.
  • The easiest way to do this is to use a continuous CO2 measurement. It is carried out with a simple mechanism permanently installed under water. However, the measurement results are purely qualitative: too much, too little or sufficient.
  • You can determine the exact values ​​with a drop test, which you can get from specialist dealers.
  • You carry out professional measurements with electronic measuring devices. Because of the high acquisition costs, these devices are rarely used in the hobby area.

You can determine CO2 in the aquarium by:

  • drop test
  • CO2 continuous measurement
  • meter
  • CO2 computer Aquarium

Is too much or too little CO 2 in the aquarium harmful?

In a rather weakly lit community aquarium with only a few aquatic plants, CO2 values ​​that are too high may arise. The metabolism of the plants is slowed down by the low incidence of light. The excretions of the animals produce more CO2 than the plants can metabolize.

Excess carbon dioxide escapes through the surface of the water. Scum or insufficient water movement on the surface, however, impair the natural gas exchange. Dangerously high CO2 values develop, which in the worst case leads to the death of your aquarium inhabitants.

How is CO 2 regulated in the aquarium?

If the carbon dioxide values ​​in your aquarium are too high, you can easily remedy this by installing a diffuser on the filter outlet. Alternatively, an air stone can be used. The most important thing is that there is movement in the water surface. This means that no scum can form and the gas exchange runs optimally. In addition, it is advisable to plant additional aquatic plants that metabolize the CO2.

If the carbon dioxide values are too low, you will find various types of CO2 substitution in specialist shops. You can start with simple aquarium CO2 tablets and biological CO2 systems up to the aquarium CO2 system that is operated with exchangeable gas bottles.

A replaceable CO2 bottle in the aquarium is the most cost-effective option in the long term. But if you prefer to experiment with the biological balance between vegetation and stocking, biological CO2 systems or CO2 tablets are a good interim solution.


How to reduce high CO2 values:

  • Sparkling stone
  • More water plants

Too low CO 2 values:

  • Biological CO2 system
  • CO2 tablets
  • Use more animals

8. Oxygen (O2)

Oxygen (O2) is probably the most important (vital) value in the aquarium, because without it, neither fish, nor plants, nor useful bacteria, which rid the water of pollutants, can survive. Oxygen enters the pool water mainly through plants (during the day), the water surface and additional technology such as aerators and air stones.

FACT: If you want to measure oxygen in your aquarium, you should do so in the morning after switching on the aquarium lighting.

Like all plants, your aquatic plants produce oxygen through photosynthesis during the day. When plants breathe, carbons are oxidized and the carbon dioxide that is no longer required is excreted. 

So the O2 content of your aquarium water reaches its lowest point in the morning. If you then measure the oxygen concentration in the water, you can be sure that it will no longer fall below this value.

What do I do if there is not enough oxygen in the aquarium?

If your fish “gasp for air” on the surface of the water or the O 2 values ​​are in the cellar, urgent measures are required.

  • Practical as a first aid measure: oxygen tablets from specialist shops.
  • If you don’t have it to hand, take a glass of water from the aquarium several times and pour it back – this brings oxygen from the air into the water. Next, clean your aquarium filter. A well-functioning filter ensures that the CO 2 values ​​in the aquarium do not rise excessively.
  • Then measure the water values. Caution: a CO2content of more than 20 mg / l cancauseCO2poisoningin some aquarium inhabitants!

Also pay attention to the nitrite and nitrate levels. Nitrite poisoning produces the same symptoms as a lack of oxygen. The pH value should also be checked. Then change the water as soon as possible. By partially changing the water with treated water, you “dilute” the concentration of the substances dissolved in the water – just like it happens in nature when it rains.

What happens to my fish if there is too much oxygen?

Oxygen overdose in the aquarium? The saturation value of oxygen in water is 7 to 8 milligrams per liter, depending on the water temperature. Your aquatic plants then secrete small oxygen bubbles on the leaf edges. After a while these peel off and rise to the surface. They vanish into thin air.

  • An excessive amount of Oxygen in the tank does not have a direct impact on the fish. The aquarium regulates itself naturally – provided the water is moved slightly.

CLAIM: Some people claim that too much oxygen suppresses plant growth and promotes algae growth. Algae are plant-like organisms that carry out photosynthesis in the same way as other aquatic plants.

Why then should high O2 values ​​have different effects on algae than on other plants? Algae tend to multiply excessively if the CO2 values ​​are too high or if there are too many rotting food remains and dead plant parts in the water. Just like in nature, over-fertilized water in the aquarium leads to a shortage of oxygen because of the many microorganisms that consume O2 – and often to algal blooms.

9. Temperature

FACT: For most tropical ornamental fish, the “comfortable temperature” is between 24 and 26ºC. Depending on the species, they can also cope with an aquarium temperature of 22 to 28ºC. Shrimp, small crabs and cold water fish like it much cooler.

TIP: When you populate your aquarium, you should definitely read the profiles of your respective favorites. This ensures that all of your animals have the same demands on the temperature in the aquarium.

These factors have an impact on the water temperature in the aquarium:

  • room temperature, possible fluctuations in day / night
  • Location: high, low, near heat sources, on exterior wall
  • Sunlight
  • size of the tank
  • In large aquariums: heat storage such as large rocks, etc.

The following aquarium thermometers are available from specialist retailers:

  • Liquid thermometer: preferably made of plastic, always without mercury, inexpensive
  • Thermometer strips glued on the outside: cheap goods, also measures the ambient temperature
  • Digital thermometer with temperature sensor in the water, display outside: top measurement results
  • Digital thermometer in water: top price-performance ratio, good measurement results

How to lower the temperature in the aquarium:

  • Put the lighting phase into the night
  • Open the cover
  • Ice cubes in an emergency
  • Change the water with cold water in an emergency
  • Use the aquarium fan
  • Install the aquarium flow cooler

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