Water values for water plants in detail

If we transfer this Liebig’s Law of the Minimum to the aquatic field it quickly becomes clear how important balanced fertilisation is for plant aquariums and how important the coordination of the fertilisation with the lighting intensity, the initial values of the water being used, the biomass of the plants and with that the daily consumption of the nutrients is.

More about this subject you will find in our series Fertilization is not just fertilization Part 1 и There’s more to fertilization than you’d think Part 2 .

So let’s have a look at the functions of the nutrients in the plant cells using some examples.


As well as enough CO2, aquatic plants need iron and trace elements to survive. Vigorously growing aquatic plants are constantly consuming iron and other trace elements. Despite their bonding to so-called chelators, as is usual in modern fertiliser preparations (e.g. JBL PROFLORA Ferropol , JBL ProScape Fe +Microelements ), these elements keep only for a limited period. The iron content needs to be checked on a regular basis with the JBL PROAQUATEST Fe Iron and, if necessary, re-fertilised. For healthy plant growth a concentration of 0.1 – 0.2 mg/l (ppm) is already sufficient. Values up to 0.5 mg/l (ppm) can be necessary for very plant dominated aquariums. The iron content can also be checked with the JBL PROAQUATEST Fe Iron in tap water (usually iron-free) or in natural waters and garden ponds.

Recommended action

< 0,1 mg/l : Dosing of JBL PROFLORA Ferropol или JBL ProScape Fe +Microelements

> 0.5 mg/l : Water change and adding of JBL Biotopol

How to test?



The degrading or mineralisation process of all organic substances (food and plant remains, fish excrement) in the aquarium and pond goes through the following stages; proteins > ammonium > nitrite > nitrate. Specific bacteria are responsible for this process. By measuring the intermediate stages of ammonium, nitrite, nitrate, conclusions can be drawn about the “functioning” of the systems “aquarium” and “pond”. Ammonium and nitrite should not normally accumulate above concentrations of 0.2 ml/l (ppm). If this is the case there may be a disturbance in the bacterial balance. A continuous increase in the nitrate content, especially in the aquarium, accompanied by a low or undetectable ammonium and nitrite content, is characteristic of a well-functioning bacterial balance, however also indicates an insufficient balance within the aquarium (too many fish, not enough nitrate-consuming plants, too few water changes). In heavily planted aquariums without fish or with only a few small fish the opposite may happen: nitrate becomes a deficiency and needs dosed additions for the plants to thrive and grow. This is especially the case with so-called aquascaping, a specialized trend to create underwater landscapes in the aquatic field. If phosphate is present in the water in addition to nitrate, levels of nitrate which are too high promote the growth of unwanted algae. This is why the nitrate content of the water should be kept below 30 mg/l (ppm) in freshwater.

Recommended action

< 10 mg/l : Dosing of JBL ProScape NPK Macroelements или JBL ProScape N Macroelements

> 30 mg/l : Water change and use of JBL NitratEx , JBL BioNitratEX или JBL Clearmec plus

How to test?



Phosphate, an important plant nutrient, only occurs in very low concentrations in natural waters. The average values are around 0.01 mg/l in freshwater. Plants and algae have adapted to these meagre levels and only require minimal amounts of phosphate. In aquariums, phosphate primarily enters the water as a result of the digestive processes of the fish or in the form of food remains. If conditions are unfavourable (particularly in heavily populated aquariums), the phosphate levels may reach values that are sometimes 100 times higher, and more, than natural levels. This inevitably leads to an explosion of undesirable algae. By regularly measuring the phosphate concentration using the JBL PROAQUATEST PO4 Фосфат Sensitive this threat can be recognised and prevented with the appropriate measures. It is important to know that algae can store considerable quantities of phosphate, enabling them to continue to grow even after the level of phosphate in the water has been reduced. Therefore the sooner the danger of a rise in the phosphate content is identified, the better the chances of quickly averting an imminent plague of algae. In freshwater aquariums values up to 0.4 mg/l can still be accepted. Better are values up to 0.1 mg/l. In heavily planted aquariums without fish or with only a few small fish the opposite may occur: Phosphate becomes a deficiency and needs dosed additions for the plants to thrive and grow. This is especially the case with so-called aquascaping, a specialized trend to create underwater landscapes in the aquatic field.

Recommended action

< 0.1 mg/l : Dosing of JBL ProScape NPK Macroelements или JBL ProScape P Macroelements

> 1.5 mg/l : Water change, addition of fast growing plants and the use of JBL PhosEx rapid или JBL PhosEx ultra

How to test?

JBL PROAQUATEST PO4 Фосфат Sensitive


Carbon dioxide (CO2) is the most important plant nutrient. In aquarium water without a CO2 supply values mostly adjust between 2 and 4 mg/l. However, an optimal value between 15 and 30 mg/l is recommended, and 20 – 25 mg/l have proved to be the best values of all. This value is harmless for fish and also ensures thriving plant growth. Therefore adjust your CO2 fertiliser system bit by bit to reach this value. How much CO2 needs to be added to your CO2 fertiliser system to reach it depends on various factors. Together with the direct consumption also the water movement and the lighting intensity (more light promotes a faster plant growth which increases the demand for more CO2) have an influence on it. Therefore the correct quantity needs to be individually calculated for every aquarium. Please also follow the operation instructions of your CO2 fertiliser system. Aquariums with few or no plants which, for example, are preferred for the keeping of fish from Lake Malawi or Lake Tanganyika don’t need an additional CO2 supply.

Recommended action

< 20 mg /l : Reduce the surface movement and use a PROFLORA Bio -, Одноразовые (u) - or Многоразовые (m) - CO2 fertiliser system

> 35 mg/l : Aerate the aquarium with Компрессоры such as the JBL PROAIR a50 or the JBL PROSILENT a400 and ensure a strong surface movement

How to test?



Along with calcium, magnesium creates the general hardness. Magnesium is, like potassium, a macroelement, which is necessary for healthy and vigorous growth in plants. Tap water (also with water with high general hardness) very often contains only too low quantities of magnesium for aquatic plants, quickly causing deficiency symptoms. The symptoms of a magnesium deficiency resemble those of an iron deficiency. Yellowish bleaching areas (chlorosis) occur between the leaf veins which can become much more intensive than during an iron deficiency. Curvature of the leaves is another symptom. This is not only limited to old leaves but appears also on freshly grown leaves. Despite a regular fertilisation of the aquarium water (e.g. once a week) it is possible that magnesium is only available in too low quantities so that the plants stagnate in their growth. We recommend first a daily measurement of the magnesium content. This way the plants’ needs can be determined and the fertiliser can be dosed appropriately. After that you can continue the routine measurements less frequently. For good plant growth the value needs to be between 5 and 10 mg/l.

Recommended action

< 5 mg/l : Use of JBL Aquadur or addition of JBL ProScape Mg Macroelements

> 10 mg/l : Mix your aquarium water gradually with reverse osmosis water or deionised water with the next water change

How to test?

JBL PROAQUATEST Mg Magnesium Fresh water


Depending on origin and consistency of the subsoil, water may contain varying quantities of alkaline earth salts. Due to the effects of CO2, a large proportion of these salts is in the form of carbonate. By definition, the proportion of calcium and magnesium salts in the form of carbonate is described as carbonate hardness. As a rule, the carbonate hardness is lower than the general hardness value. In exceptional cases, e.g. in many tropical waters, the carbonate hardness can be higher than the general hardness. Most freshwater fish and plants in the aquarium can successfully be kept with a carbonate hardness of about 3-15°d. For an ideal CO2 fertilisation the carbonate hardness should not be lower than 4-5°d.

Recommended action

< 4 °dKH : Dosing of JBL Aquadur Malawi/Tanganjika

> 8 °dKH : Add in several steps JBL pH-Minus или gradual mixing of the aquarium water with reverse osmosis water or deionised water

How to test?



Potassium is one of the macro-elements which plants in freshwater absorb quickly and effectively within a few hours and can also store for a limited time. Growing plants require more potassium than other elements. As a result, potassium concentrations can drop to a minimum range, causing plant growth to stagnate, even if the aquarium water is fertilised regularly (e.g. once a week). Potassium levels in mains water are usually too low compared to those in natural biotopes, particularly in relation to calcium and magnesium concentrations. We first recommend a daily measurement of the potassium content of your aquarium water. This way the plants’ needs can be determined and the fertiliser can be dosed appropriately. After that you can continue the routine measurements less frequently. For a good plant growth the value should approximately be between 5 and 10 mg/l, for aquariums with high power light from about 1 W/l illuminance between 10 and 20 mg/l. Higher potassium levels in the aquarium favour the growth of green thread algae.

Recommended action

< 10 mg/l : Dosing of JBL ProScape K Macroelements

> 30 mg/l : Water change and, if required, mixing of aquarium water with reverse osmosis water or deionised water

How to test?



Silicon is one of the most common elements in the world. As a result of the weathering of silicate rocks, silicon is washed into surface and ground water in the form of silicate. Mains water can therefore contain varying amounts of dissolved silicate. Mains water can contain up to 40 mg/l and, on rare occasions, even more. Silicate is non-toxic and there is no threshold set in the regulations governing the quality of drinking water. In aquariums silicon provides a nutrient for algae (diatoms), some aquatic plants (e.g. hornwort), as well as siliceous sponges and some other invertebrates. When a new aquarium is set up brown coatings of algae (diatoms) often occur. This coating disappears when the aquarium is run in and sufficient competition from other algae and microorganisms has established itself. This also significantly reduces the amount of silicate in the water. However, such coatings of algae can often reappear, particularly in saltwater, after the water has been changed, adding new silicate.

Recommended action

0 mg/l : no need for action

> 2.0 mg/l : Use of JBL SilikatEx

How to test?


pH 6 - 7.6

The well-being of fish and the growth of aquatic plants depend to a large extent on the pH level being kept as constant as possible. The pH level plays a significant controlling role in CO2-fertilization. The CO2-concentration best suited for plants and harmless to fish is reached with a pH level around 6.8 to 7.2, provided that the water does not contain any other substances which might influence the pH level. The carbonate hardness should not drop below 4° and not significantly exceed 18° dH. This means that a simple pH measurement is sufficient to check the best possible CO2-fertilization. Precise measurements may also be required even if CO2 is not used for fertilizing, for instance for the breeding of special fish species. The JBL pH 6,0-7,6 Test is also suitable in these cases.

Recommended action

< 6.0 : Use of JBL Aquadur или JBL pH-Plus

> 7.0 : Add in several steps JBL pH-Minus , peat filtering over JBL Tormec activ or the use of a CO2 system ( PROFLORA Bio , Одноразовые (u) или Многоразовые (m) )

How to test?


© 01.08.2016
Matthias Wiesensee
Matthias Wiesensee
M.Sc. Wirtschaftsinformatik

Social Media, Online Marketing, Homepage, Kundenservice, Problemlöser, Fotografie, Blogger, Tauchen, Inlineskating, Aquaristik, Gartenteich, Reisen, Technik, Elektronische Musik

Обо мне: Seit Teenagerzeiten mit Aquarien in Kontakt. Klassische Fischaquarien, reine Pflanzenaquarien bis hin zum Aquascape. Aber auch ein Gartenteich und Riffaquarien begleiten mich privat im Hobby. Als Wirtschaftsinformatiker, M.Sc. bin ich als Online Marketing Manager bei JBL für die Bereiche Social Media, Webentwicklung und der Kommunikation mit dem Anwender der JBL Produkte zuständig und kenne die JBL Produkte im Detail.


Несколько слов о кукис перед тем, как продолжить

Сайт JBL также использует несколько видов кукис, чтобы предоставить вам полную функциональность и многие сервисы. Нам требуются технические и функциональные кукис, чтобы обеспечить работоспособность сайта, когда вы на него заходите. Мы также используем кукис для рекламных целей. За счет этого мы можем узнать вас, когда вы повторно посещаете наш сайт, таким образом мы можем оценить эффективность рекламных кампаний, а персональные кукис позволяют нам предоставлять вам напрямую персонифицированную информацию, адаптированную под ваши нужды - даже когда вы не находитесь на нашем сайте. Вы можете в любой момент определить - даже позднее - какие кукис вы разрешаете, а какие нет (подробнее по ссылке "Изменить настройки").

Домашняя страница JBL использует несколько видов куки, чтобы предложить вам все функции и многие сервисы: технические и функциональные куки нужны в обязательном порядке, чтобы всё работало во время посещения вами нашей домашней страницы. Дополнительно мы используем куки в целях маркетинга. Вы всегда — сейчас или позже — можете решить, какие куки допустить, а какие нет (см. больше в разделе "Изменить настройки").

В нашей "Политике конфиденциальности" вы узнаете, как мы обрабатываем личные данные и для каких целей мы используем обработанные данные. вы узнаете, как мы обрабатываем личные данные и для каких целей мы используем обработанные данные. Подтвердите использование всех куки-файлов, нажав на "Понятно", — и продолжайте!

Вам больше 16 лет? Тогда подтвердите использование кукис кнопкой "Согласен", и мы можем продолжить.

Выберите настройки кукис

Технические и функциональные кукис, чтобы все работало правильно, когда вы посещаете наш сайт.
Маркетинговые кукис, чтобы мы могли опознать вас на страницах нашего сайта и оценить успешность наших рекламных кампаний.