© Thomas Gade / May 2015 (updated 2026)
mikrocount® fuel Test Kit by Schülke & Mayr GmbH
mikrocount® fuel Test Kit
The test kit from Schülke & Mayr contains:
• Instruction manual
• Sterile disposable pipette
• 1 pair of disposable gloves
• Sample container for 20 ml
• Glass bottle with transparent gel (nutrient medium)
The procedure is familiar from biology lessons: a nutrient medium is inoculated with the substance to be tested, sealed, and left to develop visible cultures. The mikrocount® fuel test works in exactly the same way.
First, take a diesel sample from the tank – preferably from the bottom, as water, boundary layers and biosludge collect there. Tanks with a drain cock make this easy. On many smaller boats, you often have to push a hose through the filler neck.
Using the sterile pipette, transfer a small amount of diesel into the bottle containing the transparent gel. Close the bottle tightly and shake vigorously until the gel has dissolved and is evenly distributed. The bottle now serves as a “Petri dish”. Microorganisms multiply inside and become visible through cloudiness and discolouration.
In our tests the nutrient medium became cloudy and took on a yellowish to brownish tint.
Sample 1 (2014): Taken after engine failures caused by diesel pest. Despite adding biocide when refuelling, the sludge had spread significantly.
Sample 2 (2015): Taken from the same tank after cleaning and shock dosing with Grotamar 82. The test shows only low microbial activity.
Sample 3: From another pleasure boat with visible biosludge on the tank bottom. The test confirms moderate contamination.
Sample 4: From a seasonally used motorhome. Slightly cloudy, but only minor discolouration in the test.
Cleanliness and Temperature
For reliable results, work as cleanly as possible to avoid introducing foreign germs that could distort the outcome. The gel with the diesel sample should rest for four days at 22–28 °C. If it is cooler, the test takes longer. Plan the storage of the bottle accordingly in advance.When Is the Test Useful?
For small tanks (approx. 60 litres) on a pleasure boat, the test is often not economical because you can usually see the condition of the fuel anyway. It becomes useful with large tanks (several hundred litres) where complete emptying and cleaning is time-consuming and expensive.The test is also excellent for checking whether a shock dose of biocide has been successful. Before bunkering larger quantities from unknown sources, it can help detect contaminated fuel early.
Companies with their own fuel station (agriculture, technical museums, yacht clubs) and especially operators of **emergency power generators** in critical facilities should test their fuel regularly.
Raising Awareness
Even if the test often confirms what is already visible in a contaminated sample, it is an excellent tool for raising awareness among those responsible (fleet managers, farmers, operators of backup generators). Many people are unaware that diesel ages through oxidation and can become unusable due to colonisation by microorganisms that form biosludge.A practical test during training makes the problem visible and encourages preventive measures. This helps avoid failures or at least recognise and remedy them more quickly.
Anyone who has already experienced an engine failure due to contaminated diesel should take tank maintenance seriously. Regular checks, biocides and – where possible – switching to more stable fuels like C.A.R.E. Diesel can significantly reduce the risks.