A clear and healthy pond starts with good quality pond water. The quality of the water depends on several parameters. Whether you are an experienced pond enthusiast or starting a pond for the first time, understanding and managing the parameters is essential for a thriving and healthy pond.
In this guide, we dive into the world of water quality and parameters of your pond. We cover the six crucial values: pH, kH (carbonate hardness), GH (total hardness), ammonia, nitrite, and nitrate. You will learn what these parameters are, how to measure them, what the ideal values are, and how to adjust them. This way, you can create the perfect water quality for your pond, prevent algae formation, and keep your fish and plants healthy.
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1. The most important parameters in your pond
To determine the water quality of your pond, there are six parameters that are important to understand and monitor. We will explain these parameters further here and why you should measure and adjust these specific parameters.
The following parameters are important for every pond:
- pH value: The acidity of the water
- KH (Carbonate hardness)The concentration of carbonates and bicarbonates in the water
- GH (Total hardness)The total concentration of dissolved calcium and magnesium ions in the water
- AmmoniaA toxic substance produced by fish droppings and decaying organic material
- NitriteA byproduct in the breakdown of ammonia, also toxic to fish and other animals
- Nitrate: The final product of the nitrogen cycle, plant food and in high concentrations one for algae
The pH value: The key to pond balance
The pH value is a measure of the acidity of the water and plays a crucial role in the health of your pond.
Why is pH important
It is important that the pH value remains stable within a healthy range. A too high fluctuation in pH value can cause your pond to become unbalanced and even unhealthy for your fish.
- Biological impactInfluences the activity of bacteria and the health of fish and plants
- Chemical impactDetermines the solubility and availability of nutrients and minerals in the water
How pH affects other parameters
- AmmoniaAt a higher pH, more ammonium is converted into the toxic ammonia
- CO2A lower pH increases the availability of CO2 for plants
- MineralsThe solubility of minerals such as calcium and magnesium is affected by pH
KH and GH: The hardness duo of your pond water
Water hardness in a pond tells you how many dissolved minerals (such as calcium and magnesium) are in the water. You can compare it to the difference between hard and soft water in your household: hard water has more of these minerals, while soft water has less.
The hardness of the water in your pond is measured with two parameters:
- KH - Carbonate hardness It is the protective shield of your pond water. It measures how much carbon is in the water. It helps to keep the pH levels in your pond stable. If your KH is high enough, your pH value will fluctuate less quickly.
- GH - Total hardness is like the "vitamin score" of your water. It measures the total amount of minerals (especially calcium and magnesium) that are essential for the healthy growth of fish, plants, and other water organisms. A proper GH value ensures that everything in your pond remains healthy and can thrive.
The nitrogen cycle: Understanding ammonia, nitrite, and nitrate
The nitrogen cycle is a fundamental process that takes place in every pond. It breaks down waste materials and converts them into nitrite and nitrate. This is a natural process and this cycle occurs on its own in your pond. It is important that this process is properly initiated before you add fish to your pond.

Hazards of ammonia and nitrite
- AmmoniaVery toxic to fish, even in low concentrations. It can cause germ damage and suffocation.
- NitriteAlso toxic, it disrupts the oxygen uptake in the blood of fish.
Nitrate as food for plants and algae
Nitrate is the least toxic form of nitrogen, but in high concentrations it can lead to excessive algae growth and can also be harmful to fish. Nitrate is a good source of nutrition for plants, and they help keep nitrate levels low.
2. Measuring your pond parameters
To keep the water in your pond in good condition, it is important to regularly measure the parameters of your pond. In case of deviations, you can adjust in time and prevent problems. We explain various testing methods, how to perform them, and how to interpret the results.
Choosing the right test methods
There are several ways to measure the water values of your pond. We compare the three most common methods.
1. Test strips
A test strip is a thin paper strip that reacts to the liquid when submerged in water. Depending on the parameters, the strip takes on a certain color that corresponds to a specific value of a parameter. This allows you to quickly and easily measure different parameters in your pond. Test strips are simple and inexpensive, but they can be inaccurate and harder to read.
Voordelen:
- Fast and easy to use
- Cheap for occasional use
- No special skills required
Nadelen:
- Less accurate than other methods
- Not suitable for very precise measurements
- Can expire, which affects accuracy
2. Drop tests

With a drop test, you let the pond water react with different reagents (reactive substances). Often, you drop a predetermined number of drops into a small amount of pond water in a test tube. After 5 or 10 minutes, the reagent has done its job and the pond water will take on a certain color. Using a color chart, you can then read the value very accurately. The drop test is more labor-intensive and difficult to perform than test strips, but it provides a much more accurate picture of your parameters.
Voordelen:
- More accurate than test strips
- Cost-effective for regular use
- Can measure multiple parameters
Nadelen:
- More time-consuming than test strips
- Requires some practice for accurate results
- Reagents may expire
3. Digital meters
With a digital meter, you can quickly and accurately determine the value of a parameter. For most parameters, there are no accurate digital meters. In particular, a digital meter is suitable for measuring pH values. Fluctuations in pH values may prompt you to check other parameters as well. There are meters that measure continuously which you can place in your pond, but there are also meters that you can operate manually.
Voordelen:
- Very accurate
- Fast results
- Ideal for frequent measurements
Nadelen:
- More expensive to purchase
- Requires regular calibration
- Some meters measure only one parameter
Recommendations
- For beginners and hobbyistsBegin with a good drop test set. This offers a good balance between accuracy and cost.
- For advanced pond enthusiastsInvest in digital meters for parameters that you measure frequently (such as pH) and use drop tests for the other parameters.
Tips for accurate results
- Test always at approximately the same time of day.
- Keep test equipment clean and dry.
- Replace reagents and test strips before the expiration date.
- Calibrate digital meters regularly according to the manufacturer's instructions.
Frequency of testing
- Weekly: pH, KH, GH
- Every two weeksAmmonia, nitrite, nitrate
- Monthly: Phosphate, oxygen
- At startup and/or problemsTest daily until the problem is resolved
Is there a change in your pond situation? For example, adding fish, replacing a filter, or removing sludge from the bottom. Then perform a daily test to monitor parameters.
3. Interpreting measurement results
After measuring the water values, it is important to interpret them correctly. With the right interpretation, you know whether your pond is healthy or if action is needed to adjust parameters.
Optimal values per parameter
Compare your measurements with the optimal values for your pond type. Keep in mind that slight fluctuations are normal, especially during changes in season or weather.
Parameter | Ornamental pond | Koivijver | Plant pond |
---|---|---|---|
pH | 7.0 - 8.0 | 7.0 - 8.5 | 6.5 - 7.5 |
KH (°dH) | 4 - 8 | 6 - 10 | 3 - 6 |
GH (°dH) | 8 - 12 | 10 - 15 | 6 - 10 |
Ammonia | 0 mg/l | 0 mg/l | 0 mg/l |
Nitrite | 0 mg/l | 0 mg/l | 0 mg/l |
Nitrate | < 50 mg/l | < 50 mg/l | < 20 mg/l |
What abnormal values may mean
Are one or more parameters outside this range? This may be due to one of the following causes:
- High pHCan indicate excessive algae growth or insufficient KH
- Low pHPossible consequence of acid rain or insufficient KH
- Low KHRisks of pH fluctuations
- High GHCan lead to lime deposits on plants and equipment
- Presence of ammonia or nitriteThe nitrogen cycle has not yet started or the filtering is too low for the amount of waste substances. This can be harmful to fish and plants.
- High nitrateOn insufficient plants or biological filtration to absorb nitrates. Can lead to algae growth and health problems in fish.
When to take action
Take immediate action in case of deviation from the following parameters:
- Observable presence of ammonia or nitrite
- pH values below 6 or above 9
- KH values below 3°dH
- Sudden, large changes in a parameter
In less serious deviations, you can monitor the situation for a few days before taking action. Small fluctuations are normal and can be caused by, for example, the weather. Often, the pond's ecosystem will restore itself to balance.
By regularly and accurately measuring the parameters in your pond, you can identify and prevent problems early on. This contributes to good water quality and a healthy & clear pond.
4. Correcting and optimizing pond parameters
After measuring your pond parameters, the next step is to optimize them. In this chapter, we discuss how you can adjust the various parameters to create a healthy and balanced pond environment.
Correcting pH value: Techniques and products
The pH value of your pond is crucial for the well-being of fish, plants, and beneficial bacteria. Correcting the pH must be done carefully to avoid stress for the pond inhabitants.
Methods to increase pH
- Add limeA natural method to raise the pH is by adding lime (calcium carbonate). This increases both the pH and the KH value
- pH increasersThere are special products available that quickly and effectively raise the pH
- Clean shell sandThis works slower but has a long-lasting effect
Methods to lower pH
- BluNature Carbon FertilizerAdd to pond or filter and gradually lowers pH values in a natural way
- Natural peat: Add peat blocks or flakes to your filter to gradually lower the pH
- pH-lowering productsThese are effective for a quick pH drop, but use them in moderation
- Regular water replacementThis can help with stubbornly high pH levels
Natural vs. chemical solutions
Natural methods are preferred because they work more gradually and are less likely to cause sudden fluctuations. Chemical solutions are more effective for quick fixes, but caution is advised here. Chemical solutions can be harmful to fish and/or plants. Always consult the label for use in your pond.
Precautions when adjusting pH
- Never adjust the pH by more than 0.5 units per day to prevent stress in fish
- Regularly measure the pH during the adjustment process
- Ensure adequate ventilation during pH adjustments
- Consider treating a portion of the pond water first as a test
KH and GH increase: Creating a stable water hardness
A stable water hardness is essential for a healthy pond. Both carbonate hardness (KH) and total hardness (GH) play an important role in this.
Products and methods to increase KH
- BicarbonateSodium bicarbonate (baking soda) can quickly increase the KH
- Crushed coralThis dissolves slowly and gradually increases the KH
- Special KH risersThese products are specially developed for ponds and aquariums
Techniques for increasing GH
- Epsom saltThis increases the magnesium content and thus the GH
- Oyster shellsThese dissolve slowly and increase both the GH and the KH
- GH-increasing productsThese usually contain a mix of calcium and magnesium salts
Balancing KH and GH for optimal pond conditions
- Aim for a KH between 4-8°dH and a GH between 8-12°dH for most ponds
- Keep the KH always above 4°dH to prevent pH fluctuations
- Adjust KH and GH gradually, just like with pH adjustments
Supporting the nitrogen cycle: Controlling ammonia and nitrite
One good functioning nitrogen cycle is essential for converting toxic waste materials into less harmful forms.
Optimizing biological filtration
- Increase the filter surface areaUse filter material with a large surface area for bacterial growth
- Ensure sufficient circulationThis prevents dead zones in the filter
- Regular maintenanceClean the filter carefully without removing all the good bacteria
Use of bacteria to accelerate the nitrogen cycle
- BluNature Starter BacteriaThese are essential when starting up a new pond
- Nutrients for bacteriaSome products contain nutrients that stimulate the growth of beneficial bacteria
- Replacing filter materialsqueeze the old filter mat over the new filter mat, this way you start with a bacterial culture in your new filter mat
Emergency measures for dangerously high ammonia or nitrite levels
- Immediate water replacementRefresh 30-50% of the water at high values
- Use of detoxification productsThese temporarily bind ammonia or nitrite. Zeolite helps with the absorption of toxic substances such as ammonia
- Reduce the feedingLess feed means less waste
- Increase the aerationThis supports bacterial activity. You can increase aeration with a waterfall, fountain or air pump
Controlling nitrate: Preventing algae growth
Although nitrate is less toxic than ammonia and nitrite, high nitrate levels can lead to excessive algae growth and health problems in fish.
Natural methods to reduce nitrate
- Plants in the pond: add more plants to absorb high nitrate levels
- Floating plantszoals water hyacinth or duckweed, quickly absorb nitrate
- Marsh filter: a separate section with marsh plants can effectively remove nitrate
- Biological filterincrease the filter surface and allow bacteria to break down nitrate