Freshwater Aquarium Water Quality

Freshwater aquarium water quality parameter is the most vital factor of the aquarium organisms. It governs all other parameters in aquarium and finally it impacts the health of fish and aquatic plants. The effective and sound aquarium relies on upon great water quality, appropriate feeding and general care. Most fish health issues are brought on by poor water quality and many components can make this fall apart, including: the age of the aquarium, deficient filtration, improper management, stocking densities, overfilling, etc.


The life of fish in an aquarium essentially relies on upon two elements: the condition of their natural habitat, water and the quality and diversity of feeds. Water is an astonishing phenomenon of nature and it is an incredible solvent. Specifically, it contains a large number of gases.

The wellbeing and life of the aquarium inhabitants rely on upon the temperature, wate​​​​​r pH, water hardness, salinity, dissolved gasses etc. In addition to hydrochemical indicators, the inhabitants of the aquarium are influenced by electric and magnetic fields, ionizing radiation, pressure, gravity, light, temperature, the span of living space and other abiotic factors.

The principle hydrochemical indicators of water, suitable for most aquarium fish are given in the following table. The majority of these indicators are in direct reliance on each other, and with increasing or decreasing one or two of them in the aquarium, biological equilibrium is troubled.

Reference level (mg/l)

Dissolved Oxygen (DO),


Carbon dioxide (CO 2)

Up to 8,0

Hydrogen Sulfide (H2S)


Water pH


Water temperature

​72 to 82 ​°F (​22-​28°C)

Total hardness

6.0-12.0 dGH

Ammonium( NH4 )

Up to 0,2


Up to 0.2

Nitrate( NO​​3)

Up to 0.5



Iron total( Fe)


Chloride( Cl )

Up to 2.01

Sulphate( SO4)

Up to 2.0

In the aquarium, water is enriched with gasses:

  • Through the surface;
  • As a consequence of the action of creature living beings;
  • With the assistance of unique specialized devices (aerators, filters) and aquarium equipment. Gasses disintegrate in water through the surface and when air bubbles go through the filter. The fundamental parameters that decide the condition of the fish habitat are pH, oxygen, carbon dioxide, hardness, hydrogen sulfide, methane, temperature etc.

Water Temperature

Temperature is the most important physical parameter which influences the aquarium life forms. Immune system of fish can be influenced because of sudden changes of water temperature. It additionally impacts other physico-chemical parameters of the water. Temperature changes can also influence the behavior of aquatic living beings. Plants are additionally influenced by water temperature since temperature represses plant breath and photosynthesis. For ideal fish health, freshwater tropical aquariums should be kept at around 77 degrees F but they can easily survive under temperature which ranges from 72 to 82 degrees F. Normal support of aquarium water, including close consideration regarding water temperature, will guarantee that your freshwater tropical fish remain healthy. To maintain the perfect water temperature, you would need the perfect Aquarium Thermometer.

Water pH

The life of natural biological organisms in water is fundamentally dictated by the dynamic response of water. The indicator of the dynamic response of water is given by the number of hydrogen ion H+ and is known as the hydrogen pH index. The scale of pH indicators is a straight line from 0 to 14, where the number seven means unbiased or neutral water, this figure is also called the hydrogen index. To one side of the hydrogen index are acidic waters (weakly acidic – acidic – strong acid), to another side – alkaline (slightly basic – alkaline -strongly basic). Life in water is conceivable within a pH range of 3.5 – 10.5. In aquarium, the pH usually ranges from 6.0-8.5. In messy or dirty aquariums, at the base pH can reach up to 5.4. 

pH is one of the most important indicators of the state of water in the aquarium. pH is exceptionally versatile. It relies on upon the temperature of water, the crucial movement of plants, on lighting, on the level of portability of water in the aquarium. It can vary within 2 units within a day.

During the day, the pH values change definitely in layers of water. In the upper layers, during plant photosynthesis, the pH can rise to 10-11, while at the base it will stay stable (say, around 6.6), and in the column layers, it will differ from 6.5 (during the evening) to 7-8 (Toward the evening). Changes of pH from 6.5-11 during the daytime for a living organisms are hazardous. At pH 10-11, the fish drop to the lower layers, and the plants that give rise to such alkalization of water will start to break down in the near surface layers.

The fluctuation of pH relies on upon the temperature of the water: with expanding temperature, it decreases. For instance, if the pH indicator is measured at 0 °C, neutral water should not be counted as water not with pH 7, but with a pH of 7.97 (almost 8); Therefore, water having a pH of 7 at 0 °C will already be weakly acidic.

Depending on the ratio to the concentrations of hydrogen and hydroxyl ions, all biological organisms are divided into:

  • Stenoionic (resistant to slight fluctuations in pH);
  • Euryionic (ready to withstand vast changes in pH).

The most reasonable water for most aquarium organisms should have a pH fluctuation of around 7. This is achieved chiefly by appropriate care of the aquarium, the regular substitution of some portion of the water, the cleanliness of the aquarium. pH meter is essential device to check the fluctuation of pH in aquarium. Every aquarium owner should have best pH meter that is available in pet fish market at reasonable price tag. 

Dissolved Oxygen (DO)

Oxygen is an essential to life in the aquarium, without it or if there isn’t sufficient of it just the fish will die rapidly. There are many variables which affect the level of dissolved oxygen some of which greatly affect aquarium water.

Water is soaked with oxygen because of photosynthetic action of plants. Furthermore, oxygen enters the water from the air. A large portion of this gas is soaked with the upper layer of water in the aquarium. 

The base level of DO can vary from fish to fish. General level of DO is given below:

  • For cold water fish: 6 mg/l
  • Tropical fish: 5 mg/l
  • Marine fish: 5 mg/l

​If the levels fall beneath this for delayed time frames then the fish will victim to different anxiety related diseases, for example, fin rot, white spot or other bacterial contamination. ​

A DO content of 5-7 mg/l is adequate. For instance, a freshwater aquarium with a temperature of 75 ​°F can disintegrate 8.4 mg/l of oxygen. A saltwater tank with a temperature of 82.4 ​° F and a saltiness of 15 ppt can break down 7.18 mg/l of oxygen. The above levels demonstrate 100% immersion, the greatest conceivable. The normal immersion in an aquarium is around 70%.

Generally dissolved oxygen level becomes higher during the day time due to photosynthetic activities of plants and it is reduced in the early morning hours. The Best Aquarium Air Pumps is very very important for this reason.

Carbon Dioxide (CO2)

Carbon dioxide is basic to plant development. Carbon dioxide in its purest frame is a gas, however like oxygen it can be promptly dissolved in water. Aquarium plants use this dissolved carbon dioxide through the process of photosynthesis. Flora and Fauna initiate carbon dioxide in the process of respiration. Maximum fish do that thru the gills.

Aquarium plants require lighting, manures and CO2. These are basic elements representing the speed of development and well-being. To distribute of CO2 evenly in your aquarium, a COdiffuser is used, if you have planted aquarium. Because plants need sufficient COto perform photosynthesis for making food. If you use aquarium diffuser that helps to evenly disperse and break down of big CO2 bubbles to tiny bubbles suitable for performing photosynthesis.  

When CO2 increases in the water, it depletes the pH and makes water acidic. This Issue regularly happens around evening time, photosynthesis does not occur due to lack of lighting. This CO2 being added to the water of the aquarium and pH drops quickly and affects aquarium fish. CO2 addition in the aquarium should be nearly observed. 

Increase the concentration of carbon dioxide in the water, extreme accumulation of plants and fish. In a few fish, an advance in the concentration of carbon dioxide causes an increase in urge for food. During the photosynthetic activity of plants, CO2 is removed from the water. The quantity of it decreases with increasing temperature and salinity of water. For maximum animal organisms, carbon dioxide is toxic. 

The shortage of ​CO​2 in aquarium water adversely influences aquarium plants ( Cryptocoryne, Echinodorus, etc). In the environment, such aquarium plants without difficulty soak up carbon dioxide in pure form. Whilst immersed in water, they trap carbon dioxide from the water in the course of photosynthesis.

Water Hardness

The hardness is the essential indicator of water. It is the measure of dissolved mineral salts in the water. This indicator is controlled by the presence of calcium and magnesium particles in water. There are two essential sorts of hardness of significance to aquarists, named general hardness (GH) and carbonate hardness (KH). The General hardness and carbonate hardness independently affect the water in various ways. 

Fish are clearly influenced by general hardness. It affects on cell membranes, internal organs development, especially on kidney. Carbonate hardness is on occasion called “temporary hardness” since it can be removed from water by percolating which empowers out the carbonates. Calcium hardness has no quick impact on fish; it buffers the pH by additions of acids or bases, keeping the pH stable. With the change or elimination of temporary ​hardness, the total hardness of the water also decreases.

In hydrochemistry, water hardness is expressed in milligram equivalents of calcium and magnesium; 1 mEq contains 20.04 mg/L of Ca or 12.5 mg/L of Mg. In organic chemistry, this indicator is generally expressed in degrees. At present in aquarium literature, it is standard to express inflexibility in German degrees dH (from the words “German toughness”).

In hard waters containing calcium compounds, plants discharge carbon dioxide from carbonate substances in the daytime. This procedure happens in the form of complex chemical reaction during which a Ca​CO​3 calcium salt is formed.

Lessening the amount of carbonates in the water prompts an abatement in its hardness and is called biogenic softening of water. It is the higher the better illuminated in the aquarium plants. Since the total hardness relies on upon the carbonate. In poor light, and furthermore around evening time, some portion of the Ca​CO​​3 salt again goes into the condition of the ionic solution.

The hardness of water is particularly strongly fluctuating when it “blooms.” Large variations in time and general hardness can unfavorably influence the health of the fish of the aquarium.

In soft water, the Ca​CO​​3 salt responds with carbon dioxide and fundamentally changes the pH.

Hardness of natural water is divided into following types:

  • very soft (2-4 ° dGH);
  • soft (4-11 ° dGH);
  • medium hardness (11-22 ° dGH);
  • hard (22-34 ° dGH);
  • very hard (more than 34° dGH).

Hydrogen Sulfide (H2S)

It is happened in maturing aquarium system during the activities of micro organisms such as bacteria and micro-organisms that reestablish sulfates in water. Hydrogen sulfide is very dangerous that diminish the concentration of oxygen in the water.

Marsh Gas (methane)

This gas is occurred in bottom layer of the water body, which is created from the decomposition of dead animal life forms and plant parts.

Both hydrogen sulfide and marsh gas are harmful to most aquarium occupants. 

Numerous natural procedures happen in water bodies, changing the chemical behavior of water and soaking it with natural substances. The totality of every one of these substances decides the compound organization of the water in the aquarium. ​

Also Read: How to Maintain Ammonia Level in a Goldfish Tank

Soil for the Aquarium

Soil is an imperative part for a full promised aquarium. It is fundamental for plant development since soil get roots from plants and supply essential supplements. Soil acts as a home of valuable microscopic organisms and protozoa. Soil adds to the progressing life forms in the aquarium. The soil is steadily loaded with natural particles and microorganisms which are changed into a dynamic biological environment in which waste material is processed and super nutrient soil is made which is suitable for ideal growth and advancement of plants.

The soils have following basic requirements:

  • It should serve as a fundamental supplement medium for microorganisms and plants;
  • ​The soil must be permeable in structure;
  • In the ground of the aquarium, there should not be a considerable measure of calcareous rocks, and furthermore noxious substances;
  • The color of the soil should be dark. Because light reflect light which prompts a temperature difference between water and soil;
  • The best soil for an aquarium is the dark coarse-grained river sand. It is significantly less demanding to clean, so it ​should be given preference. The darker the ground, the more differentiated the fish and plants on its background;
  • Very fine sand is unacceptable for the aquarium, since it is firmly hardened, the water circulation to the plant roots stops, and the roots decay, while harmful hydrogen sulfide for fish is discharged;
  • Particles of the soil (sand) ​should have a size of 1.5-3 mm, and at times significantly more;
  • Gravel and rock with particles up to 8 mm can be utilized if aquarium plants have a solid root ​system;
  • Large sand and rocks are utilized for the substance of goldfish, certain types of catfish and different types of fish burrowing the sand;
  • In an aquarium with plants that have a gentle root system, in this case, medium-grained sand is ideal:

​Final verdict

Water is an amazing phenomenon of nature which influences the well-being and growth of aquarium inhabitants. To make your aquarium environment healthy, good water quality is essential. In this case, you should always monitor water chemistry parameters using best water test kits for successful fish keeping. Because poor water quality causes fish diseases.  Hence it is our obligation to ensure that their water is in suitable condition.

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