Why is the water in your pond or pond green?

Why and how to fix green water in your pond? This green water is mainly due to the appearance of microalgae. In fact, it is phytoplankton: unicellular algae that should not be confused with filamentous algae.

Green water is very often present in new ponds, and more particularly in those that have water rich in nutrients.

Why is the pond water green?

Green water appears mostly during the spring. When temperatures start to warm up to around 14 degrees, phytoplankton forms. Heat therefore amplifies the imbalance of the pond ecosystem, but it is entirely natural.

In addition to strong sunlight and the warming of the water, other causes can be added to this, such as a nitrate spike, often due to:

• Overpopulation of fish in the pond, a lack of plants,
• An accumulation of organic waste, often due to leaves falling in autumn and winter.
• Also, a lack of oxygen in the pond and stagnant water.
• Another cause is the use of a filter that is not efficient enough for the size of your pond and insufficient regular water renewal. You should change 10% of your pond's volume per week. Cloudy green water is not toxic in itself for your fish, but it can cause significant variations in oxygen and pH at night. It also helps protect them from sunburn.

Solutions proposed to avoid green water in the pond

The use of products

The first solution, and often the first reflex, is the use of products. If you look closely on the Internet, the advice you find is often written by manufacturers who are looking to sell their products.

That said, before any intervention, the ideal approach is to work on the causes that led to the appearance of green water. This is an important step because, obviously, the phenomenon will likely return as long as the real causes have not been found and treated.

The use of pumps and filters

There are other systems that help mitigate this effect: the use of a pump and filter, increasing the number of plants (also beneficial), and trying to create as much water movement in the pond as possible.

⭐ You might be interested in: we show you how to choose your pond pump.

In summer, lakes and ponds are green because, obviously, there is no filtration system. A fish population that is difficult to regulate is very often accompanied by a lack of oxygenating plants and very insufficient water circulation. Conversely, rivers and waterfalls are not prone to greening because the water is not stagnant and is not in a closed circuit.

⭐ You might be interested in: our detailed article explains how to choose a filter for your garden pond.

The use of a UV sterilizer

Using a UV sterilizer is another solution, and the most effective of all. On the other hand, the downside is electricity consumption; indeed, you should count on about 3 to 5 Watts per cubic meter of water, depending on the dimensions of your pond.

⭐ You might also be interested in: our collection of ultraviolet devices

To date, it is really the only solution that can be described as truly effective for fighting green water.

Attention: this requires the use of a pump, of course, adapted to the flow rate of your UV sterilizer. This is the best ecological solution compared to using algae treatments.

Finally, the annual electricity consumption of a UV sterilizer will cost you much less. This is contrary to using multiple products that will only work temporarily, knowing that these products will also have an impact on the local fauna and flora.

Conclusion

Green water is not toxic in itself for your fish or your pond, but it can cause strong variations in oxygen and pH at night; as for the rest, it is mostly an aesthetic issue. It also helps hide your fish from predators.

⭐ You might be interested in: the list of oxygenating plants to keep a pond balanced

If you are more into organic or natural methods, you will leave your pond with green water. However, if you really want crystal-clear water, the ideal approach would be to use a UV sterilizer, which is one of the best alternatives.