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    Water tests in a planted aquarium

    Which tests do you need for an Aquascape?

    In our series of articles "fertilizing a planted aquarium part 1 to 3" we have already covered the basics of aquatic plants nutrition. There are many different water parameters such as pH value and total hardness which can be determined using apt water tests. If the focus is on the keeping of aquarium plants, certain tests, useful for these purposes are recommended. We show you, which water tests should be purchased as an aquascaper or plant aquarist and which are more or less unnecessary.

    In general, an ambitioned aquascaper shouldn’t shy away from spending the money for qualitatively good single tests. These are usually based on the droplet method of measurement. Hard to read tests or stripe tests are less suitable to determine exact results.

    Crucial water tests

    In the following we will list high-priority tests that shouldn’t be missing in your repertoire if you want to delve deeper into water plant aquaristics.

    CO2 test

    Carbon is one of the most crucial nutrients for plants which is often only insufficiently available in an aquarium. To accelerate plant growth, carbon usually gets supplied by the use of a CO2 system. The amount of dissolved carbon in the water can be determined by using a direct test. But since the CO2 saturation should at best be monitored permanently, the use of a drop checker with suitable indicator fluid makes more sense.

    Aquasabi drop checker

    A content of 20 to 30 mg/l CO2 should be aimed at, which is indicated by a green colour of the test reagent. More info on the topic of CO2 permanent testing can be found in our article "properly determine CO2 content".


    Nitrogen (N) is one of the three main- or macronutrients (NPK) for plants. Nitrogen in the shape of nitrate (NO3) is determined by a water test. The nitrate content should be at 10 to 25 mg/l in a planted aquarium. An individual-component fertilizer such as Aqua Rebell Makro Spezial N or Advanced GH Boost N can specifically lift nitrate content. A lack of nitrogen causes deficiency symptoms in the aquatic plants like yellow leaves and often coincides with a sudden occurance of green algae like thread algae

    Macherey-Nagel - Visocolor ECO - Nitrat

    Unfortunately, many common nitrate tests are hard to read, which is why we recommend the nitrate water test by Macherey & Nagel, which is a bit more costly but also much more precise in the determination of nitrate content.


    Phosphorus (P), next to nitrogen (N) and potassium (K) belongs to the so-called macronutrients as well. An appropriate test determines the content of phosphorus present as phosphate (PO4). As a rough guideline, a phosphate content of 0,1 to 1 mg/l is recommended. It is not always essential to keep up a measurable phosphate content. Depending on the situation, the phosphate content can sink relatively quickly. Since plants can store this nutrient pretty well, it is not always necessary to steadily re-fertilize. Many plant aquarists therefore rely on the principle of push fertilization: once a week, PO4 gets added until a certain target content (e.G. 0,5mg/l) is reached using a liquid phosphate fertilizer. Over the next week, the concentration is then allowed to drop to zero. It usually takes a rather long time until deficiency symptomes get visible on the plants. Stagnation in growth with reduced shoot tips may occur, or a darkening of the plants. The increased occurance of green spot algae is also often brought into connection with a lack of phosphorus.

    JBL - PO4 Test sensitiv


    Iron (Fe) is important for the formation of leaf green (chlorophyll). If there is a lack of iron, the plants will show significant so-called iron chlorosis with a bright, pale leaf colour and leaf veins staying green. Best to be seen in new growths. The addition of iron to a planted aquarium happens with the help of an iron complete fertilizer. Thus, together with other important trace elements such as manganese, boron and zinc, but also nutrients such as potassium, the micronutrient area and in some cases the macronutrient area is covered. The Fe content can be determined using an Fe water test. The target value is a content of 0,05 to 0,1 mg/l Fe. Similar to the macronutrient phosphorus, iron doesn’t have to be constantly traceable. This is partly due to the nutrient stabilization of the respective liquid fertilizer. This determines how quickly the iron contained in the fertilizer is made available to the plants. If the Aqua Rebell Mikro Basic Eisenvolldünger is used, the nutrients are stabilized much stronger and available to the plants over a prolonged period of time. This fertilizer is suitable for weekly and daily use. If using Mikro Spezial Flowgrow, the nutrients are stabilized more gently and immediately available to the plants, but also depleted quicker resp. broken down by microorganisms. A daily dose is recommended. Especially with this kind of liquid fertilizer, the added iron might not be traceable after mere hours.

    If there is too little or too much iron in the water can be seen with the naked eye. A lack of iron leads to the abovementioned symptoms. An overdose often intensifies the growth of red algae, (black beard algae or staghorn algae). An Fe water test should be the basic equipment for any less-experienced plant aquarist or as a security reference to advanced aquascapers.

    Optional water tests

    For the ambitious plant aquarist, the ratio of other macronutrients such as potassium, calcium and magnesium to optimize the nutrition of aquatic plants, will be interesting as well. This is better described in our article "the calcium-magnesium correlation". For this the purchase of individual water tests for the respective parameters naturally makes sense.


    JBL - K Test

    Useful potassium tests for freshwater have only become available recently. The recommended potassium content in a planted aquarium is between 5 and 10 mg/l potassium. Not much is consumed by this substance, but when deficient, plants show signs of necrosis (leaves full of holes). Many fertilizers such as iron full fertilizer, ready-mix NPK products and also some nitrate fertilizers supply the plants with potassium on the side. For a targeted raise of the potassium content, pure potassium fertilizers such as Aqua Rebell Makro Basic Kalium are advised.


    Magnesium tests suitable for freshwater aquariums have only been available for a short time now. Magnesium (Mg) is an often underestimated, important nutrient for aquatic plants and a momentous component in photosythesis. In tap water, unlike calcium, magnesium is only present in small amounts. A planted aquarium should contain more than 10 mg/l of magnesium, respectively, should have a certain ratio in relation to calcium. The nutrient can easily be added using epsom salt.

    Total hardness

    The total hardness (GH) indicates the total sum of alkaline earth metal cations present. These include above all the elements calcium and magnesium. If looking deeper into the calcium-magnesium correlation, it is naturally important to be able to determine the calcium content. Convenient water tests are available. But even without a test the calcium content can be deduced, if magnesium content and total hardness are known. Insofar the purchase of a GH water test is advised. A regular monitoring of the total hardness is recommended, if soft water-loving creatures like Bee Shrimp are kept, or water hardening stones are used as decoration.

    Macherey-Nagel - Visocolor ECO - Carbonathärte - TestMacherey-Nagel - Visocolor ECO - Gesamthärte - Test

    Carbonate hardness

    A not too high carbonate hardness (KH) is important for the successful keeping of aquatic plants. If water hardening stones such as Seiryu Ryuoh are used in an aquarium or aquascape, the KH will increase significantly within a week. Thus, hardness should be checked in regular intervals, using a water test. Larger water changes with soft water will help lowering carbonate hardness.

    Less important water tests

    The following tests are not quite as important for the operation of a plant-accented aquarium. But for individual cases or for a regular aquarium with a focus on fish, they are quite useful.

    Nitrite and ammonium

    During the start-up period of a newly arranged aquarium, certain strains of bacteria need to develop first, which help push forward the pollutant decomposition in the ecosystem. This includes nitrogen compounds such as nitrite (NO2) and ammonium (NH4), which can be poisonous to the aquarium’s inhabitants at certain levels, and can very much be the case during the warm-up phase. The pollutants can be determined with the appropriate water tests (e.G. with the JBL NO2 Test and JBL NH4 Test). If too high concentrations occur during the warm-up phase, you should wait with the stocking of animals. In a stable aquarium with a longer life, these substances are usually no longer detectable or only in very small concentrations.

    pH value

    JBL - pH Test-Set - 6,0-7,6

    The pH value in a planted aquarium is usually kept at a slightly acidid value below 7 by the use of soil substrate and the supply of CO2 This rough estimate is already enough for a successful keeping of aquatic plants and most tropical ornamental fish preferring acidid water. Thus the pH value doesn’t necessarily have to be monitored constantly. Should the aquarist be ambitioned to keep and breed special fish or shrimp, the exact adherence to a given pH value becomes crucial. Of course, an appropriate water test should then be at hand.
    PH value too high? Possibilities for reducing the pH value are presented in this article.


    Other water tests for parameters such as copper, chloride and silicate can be purchased if problems with those elements have occured, are suspected, or rather to rule out problems beforehand. This might be the case when using tap water. A water conditioner or the use of demineralized water (by e.G. reverse osmosis) can be a remedy.