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JBL Potassium FW Test Set

by JBL
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SKU J25411
  • For the perfect aquarium plant growth: determines the ideal potassium value to monitor the fertilisation of freshwater aquariums.
  • Quick test: fill cuvette with sample water, add reagents, fill cloudy sample water into special glass vial until underlying cross is no longer visible, read the quantity you have filled. This value is equivalent to the potassium content in mg/l
  • Use: for the ideal setting of the potassium content for perfect plant growth, especially for sensitive plants.
  • Online Laboratory: free analysis and recommendations for the water values you have measured.
  • Package contents: 1 quick test, K Potassium Test Set. Contents for approx. 25 measurements. Incl. 2 reagents, special glass vial, syringe, dosing spoon and colour scale. Refill reagents available separately.


Healthy aquariums with conditions close to nature:

  • The right water values are dependent on the fish stock and the plants in the aquarium.
  • Even if the water looks clear it can be contaminated.
  • With bad values diseases or algae can appear in the aquarium.
  • To maintain a healthy aquarium with conditions close to nature it is important to check and adapt the water values regularly.
  • For each water analysis JBL provides water tests in the form of quick tests or colour change tests.
  • These determine a certain value or several values in one go.
  • With these water tests you can recognise algae problems and negative nitrate, nitrite, potassium, magnesium values etc.

Why test?

  • Potassium is one of the macroelements 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.
  • Potassium levels in mains water are usually too low compared to those in natural biotopes, particularly with relation to calcium and magnesium concentrations.

Recommended potassium values:

  • Freshwater aquarium (community aquarium): 10-30 mg/l
  • Lake Malawi/Lake Tanganyika aquarium: 10-30 mg/l
  • Plant aquarium with few fish (aquascaping): 10-30 mg/l
  • Marine aquarium: the potassium content is not measurable with this test

You can analyse the water values you have measured in the JBL Online Laboratory free of charge and receive recommendations.


Where can I find the record sheets for the documentation of my water analysis?

> Have you lost your record sheets, already filled them all in or do you need them in another language?

With the following links you can quickly and easily print out your new record sheets with recommendations for the individual parameters at home and document the water analyses.

I have lost my colour chart. Can I download the colour chart for the test?

> The colour cards are not available for download on the JBL website. The absolutely accurate colour reproduction that is required can only be achieved using a printer which can be re-calibrated before each printout. Most privately used printers are not accurate enough for this.

You will find the colour chart bundle as a spare part on the respective product page and in the spare parts shop under:

What can I do when the measured value of a water test falls outside the scale?

> If one of your measurements reaches the end of the colour chart scale you can multiply the scale by diluting later tests with distilled water (e.g. JBL Dest).

Here’s how to do it: dilute the sample with distilled water and carry out the test once more.

This works in detail as follows:
GH test: Instead of 5 ml use 10 ml aquarium water. Now 1 drop is equivalent to 0.5 dGH.

KH test: Instead of 5 ml use 10 ml aquarium water. Now 1 drop is equivalent to 0.5 dGH.

Note: when using 10 ml sample water the colour development is weaker with the first drops than with 5 ml sample water. Put the measuring container on a white underlay for a better readability.

NH4/NH3 ammonium/ammonia, NO2 nitrite, Fe iron and Cu copper:

2.5 ml sample + 2.5 ml dist. water: result times 2

1 ml sample + 4 ml dist. water: result times 5

0.5 ml sample + 4.5 ml dist. water: result times 10

NO3 nitrate, SiO2 silicate, PO4 phosphate sensitive and Mg magnesium freshwater:

5 ml sample + 5 ml dist. water: result x 2

2 ml sample + 8 ml dist. water: result x 5

1 ml sample + 9 ml dist. water: result x 10

PO4 phosphate koi high range:

2.5 ml sample + 2.5 ml dist. water: result x 2

1 ml sample + 4 ml dist. water: result x 5

K potassium:

7.5 ml sample + 7.5 ml dist. water: result x 2

3 ml sample + 12 ml dist. water: result x 5

1.5 ml sample + 13.5 ml dist. water: result x 10

K potassium in marine water:

1. Fill 10 ml of sample water with distilled water to 300 ml.

2. Follow the instructions for fresh water.

3. Multiply the test result by a factor of 30.

CO2 direct, Ca calcium and Mg+Ca magnesium+calcium: not required.

Do my water tests still work although they have been open for nine months?

> Basically a sealed test keeps longer than an open one. How much the shelf life is reduced depends crucially on the handling and the storage conditions of the reagents. It may happen that a reagent in a test that has been open for 9 months doesn’t indicate correctly any more. However, additional information is needed to answer this question properly.