B-Load Test

The B-Load Test is used to determine the biological load of pond water (without fish). Along with other water tests it tests the fitness of pond water for fish keeping. It is qualitative test that was specially developed for assessing the water quality of both new and established ponds.


Contents of kit:

4x Test tube

2x Syringe, 10ml

1x Drip bottle, Reagent 25ml

Instruction sheet

Needed other than kit:

Clean, biologically inactive water eg bottled water as control; a cup; white paper & watch.


Use syringe S1 to fill tube No 1 with 10ml clean, biologically inactive water (Control)

Use syringe S2 to fill tube No 2 with 10ml pond water (the test sample)

Use a cup or jar to keep tubes upright.

Add 5 drops of the reagent in both tubes turn the tubes once and wait.

A colour change from purple to brown should be visible depending on the various factors.

Use a white paper in bright light to make colour change more visible.

Do not let the fluid stand in the test tubes for longer than necessary as it will discolour.

It is important to work clean and in an uncontaminated way to ensure repeatable results.



Approximate condition of water

Color change in less than 1 minute

Very high in biological activity.

Take steps to reduce the load. Failure to address problem could manifest itself as bacterial or fungal diseases or excessive parasite populations. Eg ulcers (Aeromonas hydrophila etc.), skin conditions (Flavobacterium columnaris etc), fungi (Saprolegnia spp etc), etc. More likely to happen in older, established ponds.

Could also be as the result of other toxic or non-toxic components in the water. This is more likely in new dams, after large water changes (chlorine) or influx of muddy rainwater.

Investigate the cause.

less than 10 minutes

Biological activity is still too high. Requires attention.

less than 30 minutes

Biological activity is acceptable and low in free-swimming organisms.

Longer that 30 minutes

Biological activity is very low. Water is low in vagile organisms. Water is very low in DOC or other reactive components



The Control Tube should not change in colour in 60 minutes or more. Should this happen, either the ‘bottled water’ you use as a standard is contaminated or your reagent is oxidised, contaminated or expired.


If the colour change is fast and less than one minute, diluting the sample with clean water will give a much clearer picture of the severity of the contamination.

Diluting it down until it takes about 10 minutes to change color will give an indication how serious is the biological load.

Things affecting the reaction:

DOC (dissolved organic carbon)

POC (particulate organic carbon)

Organic matter of the dead kind

Algae and other lower organisms

Bacteria, fungi, viruses

Iron or manganese

Certain chemicals



Rinse the tubes with fresh water immediately after use and turn up side down to dry. If they do stain let fill the tubes with peroxide (20%) and let it stand for a day before cleaning and drying them again.


Reason for DOC

High DOC/POC it is usually caused by the inability of the pond to remove the solid waste from the water. This is a common shortcoming in the construction design. For example if recirculating flow rate do not allow time for settlement or adequate physical filtration.  Pond owners must therefore manually perform this tedious task. As uneaten food, fecal waste, leaves and other waste of organic origin settles in the pond bottom it produces various products of decays. In some cases these mineralise into toxic gases or soluble components but mostly stay in suspended form and provide a substrate on which bacteria and fungi can flourish. As the DOC/POC increases, the higher the organism count in the water and the higher the chance of breaching the natural ability to resist infection. When the immune system is compromised for some or other reason, this is an ideal opportunity for the opportunistic bacteria to infect the fish and cause harm.

The next step is you loose control as some opportunistic organism turn virulent. Suddenly you have a problem. 

Remedial action:

If the organic load is high and you have no reason to think it is due to something else, begin by cleaning or vacuuming the pond bottom. Use a benthonic clay product like Sparkle to aid protein absorption and precipitation or use potassium permanganate solution eg Koi-PPM to aid precipitation of organics or use an antibacterial agent like SaniPond to lower the bacterial activity.


A known concentration of oxidizer is used to oxidise organic compounds and other organisms. The colour change is indicative of the reaction and biological load.

Read more here

Dissolved organic carbon (DOC) is a broad classification for organic molecules of varied origin andcomposition within aquatic systems. The "dissolved" fraction of organic carbon is an operational classification. Many researchers use the term "dissolved" for compounds below 0.45 micrometers, but 0.22 micrometers is also common, saving colloidal for higher concentrations. A practical definition of dissolved typically used in marine chemistry is all substances that pass through a GF/F filter. The recommended measure technique is the HTCO technique after filtration on precombusted glass fiber filters, typically GF/F filters



Dissolved organic carbon (DOC) is defined as the organic matter that is able to pass through a filter (filters generally range in size between 0.7 and 0.22 um). Conversely, particulate organic carbon (POC) is that carbon that is too large and is filtered out of a sample. If you have ever seen a body of water that appears straw, tea, or brownish in color, it likely has a high organic carbon load. This color comes from the leaching of humic substances from plant and soil organic matter. This organic matter contributes acids to the stream, resulting in the yellow-brown coloration as well as weathering the soils. Organic carbon can be allochthonous, or sourced from outside the system (e.g. by atmospheric deposition or transported long distances via stream flow) or it can be autochthonous, or sourced from the immediate surroundings of the system (e.g. plant and microbial matter and sediments/soils within the catchment). High amounts of organic matter are common in low oxygen areas, such as bogs and wetlands.



Call for input.

This test uses a well documented reaction but has never been used in this way to determine the health of the pond water. We tested with water from various different ponds to establish a scale that makes sense. The testing is on-going and you input is needed. We will appreciate any feedback with the test, its instructions or its reaction.


B-Load Test was developed by KoiNetof of 13 Industry Close, Gansbaai. 

Servaas de Kock