Water parameters in ponds
If you want to know how healthy your pond is, you need to keep a close eye on its water parameters. These depend on a number of different factors. Discover everything you need to know about water parameters in ponds and what these mean for your pond care measures.
© Tetra GmbH
Water parameters in ponds
For garden pond life to thrive, it requires good water quality and environmental conditions. As ponds are not natural water bodies, they need extra special care.

The water parameters are affected by many different factors – unfortunately usually to the detriment of the water quality. These include external influences such as heavy rainfall but also partial water changes using unsuitable water. Too many fish, too frequent or incorrect feeding and even the installation of pond equipment can also play a role. It is therefore important to regularly check the key water parameters as well as to test any water that you want to add to your pond.
How are water parameters measured?
Simple, safe and reliable water tests can be used to easily check water parameters. If time is of the essence or you want to check water parameters spontaneously, test strips are a particularly good solution as they measure the individual values in seconds.

Many specialist retailers also conduct pond water tests on behalf of their customers. If using this service, you should make sure that you fill a sufficiently large container with pond water, seal it without air bubbles and have it tested as soon as possible. Until given to the specialist retailer, the water should be stored in a cool, dark place.
Water parameters in ponds: pH value
A very important parameter for garden ponds is the pH value. This indicates whether the pond water is acidic, neutral or alkaline. Pond pH values can be quickly and reliably determined using a liquid test or test strips without any need for an electronic measuring device (pH meter). If the pH value is under 7, the water is classed as acidic. If it is over 7, it is classed as alkaline or base. Pond fish tend to be happiest when the pH value is between 6.5 and 8.5. As fluctuations over the course of the day are perfectly normal, you should test the pH value at different times of day.

The pH value is directly dependent on sufficient carbonate hardness. If problems with the ecosystem have led to the pH value either dropping excessively or even dramatically increasing (e.g. in the case of algal blooms), a pH stabilising agent can be used as an emergency measure. In such cases, we also recommend that you conduct one or more partial water changes.

• Good pH values in ponds : 6.5 – 8.5
Water parameters in ponds: carbonate hardness
The carbonate hardness can buffer pH fluctuations in pond water. It is not the same as the lime content as lime is water insoluble. What matters is that the carbonate hardness should remain above 3 °dH wherever possible as pH instabilities can otherwise quickly ensue. In the case of particularly intensive plant growth, algal blooms, high levels of feeding or a large fish stock, the carbonate hardness should be regularly checked. Partial water changes and stabilising water treatment agents can help prevent or rectify drastic decreases in the carbonate hardness level.

• Good carbonate hardness level in ponds : > approx. 3 °dH
Water parameters in ponds: general hardness
The general hardness of water is largely determined by the calcium and magnesium ions dissolved in it. Water is often referred to as soft if its general hardness is less than 8 – 10 °dH and as hard if this is over 18 – 20 °dH. As magnesium and calcium are important trace elements for pond fish, microorganisms and plants, the general hardness should always be sufficiently high. As for other parameters, regular partial water changes help promote good general hardness.

• Poor general hardness in ponds: very low
Water parameters in ponds: ammonium and ammonia
Ammonium (NH4+) and ammonia (NH3) are created, e.g. as a fish waste product (via the gills) but also through the decomposition of organic materials such as dead plant matter and food residues. Ammonia is created when the pH value is in the alkaline range and is poisonous to pond life. However, in ponds with a properly functioning ecosystem, ammonium and ammonia are quickly converted into nitrite followed by non-toxic nitrate.

For the aforementioned conversion to take place, biological filtration must already be in full swing. A powerful pond filter should therefore be used in any ponds with a particularly large fish stock. To ensure that the water contains enough oxygen for successful biological filtration, you should also use an aeration pump

• Good ammonium/ammonia value in ponds: not detectable
Water parameters in ponds: nitrite/nitrate

Although poisonous to fish, providing biological filtration is working properly, the nitrite resulting from ammonium/ammonia is converted into non-toxic nitrate. High nitrite values therefore indicate a problem or inadequate biological filtration of the water. Once nitrite is converted into nitrate, it is used by plants as a nutrient. As algae also like excess nitrate, however, this can quickly lead to an algae plague in your pond. At times of year when there is little (underwater) plant growth, partial water changes should therefore be used to prevent the water’s nitrate level from rising. Learn more about how to combat algea here.

• Good nitrite level in ponds : not detectable
• Good nitrate level in ponds : as low as possible

Water parameters in ponds: phosphate
When looking at substances that contaminate pond water, phosphate plays as important a role as nitrate. Phosphate mainly gets into ponds as a result of fish waste but also from rotting plant matter and leaves. Phosphates can be either dissolved into the water or chemically bound, e.g. in the substrate. A layer of sediment can therefore act as a permanent source of phosphate.

Although phosphate is a building block of life for all creatures and therefore essential, an excessively high phosphate level can also lead to an algae plague. This can only be avoided through a suitable fish stock, proper feeding with high-quality brand foods and proper pond floor maintenance. However, phosphate-reducing products from specialist retailers can also help. As a general rule, regularly removing the sediment from the pond floor, frequently conducting partial water changes and adding a sufficient stock of plants can keep the phosphate level in check over the long term.

• Good phosphate level in ponds: as low as possible
Water parameters in ponds: oxygen
The amount of oxygen that can be dissolved in pond water depends on the water temperature. The warmer the water, the less dissolved oxygen it can contain. To reveal any oxygen problems, you should test the water in the early hours of the morning as the oxygen content is lowest at this time of day. On hot and humid days in summer and in the case of intensive plant or algae growth, it is particularly important to ensure that the water is circulated by a pump or a stream, for example. The most effective solution is to use a special pond air pump, which can also be vital for the survival of your pond in the case of intensive plant growth or algal bloom. The pump should especially be used over night.

• Critical level for oxygen in ponds: < 5 mg/l with carp
Our product recommendation

Tetra Pond Test 6in1

Test strips to determine the pond water quality in a matter of seconds.

Tetra WaterTest Set

Water test set for the reliable and precise determination of five decisive water values.

Tetra Test NH3/NH4+

Measures the ammonia value reliably and precisely
AUTHOR: Tetra GmbH
DATE: 27.01.2017