Hard water in Switzerland: The right approach for your aquarium

Anyone setting up an aquarium in Switzerland will usually come up against a very specific issue very quickly: limescale. Particularly in the Swiss Plateau, the Jura or the Geneva region, tap water is often so hard that it poses a challenge for many common ornamental fish. What is excellent for us as drinking water requires a certain amount of planning and technical understanding in the world of aquatics.

To succeed in the aquarium hobby, it is crucial not to view water hardness as an insurmountable obstacle, but rather as a parameter that you can either actively manage or consciously take into account when selecting your fish.

Why Switzerland’s geology shapes our water

The water hardness in our communities is no coincidence, but the direct result of our Limestone Alps and the Jura mountain ranges. As rainwater seeps through layers of limestone and sediment, it becomes enriched with calcium and magnesium ions. In technical terms, we measure this primarily using two values:

• Total hardness (GH): The sum of all alkaline earth ions.
• Carbonate hardness (KH): The proportion that significantly buffers the pH value.

Whilst softer water often flows from the taps in Alpine regions, values in the lowlands frequently exceed 20° dH (German hardness). For soft-water fish such as discus or red neon tetras, this causes osmotic stress, which can place a permanent strain on their organs.

Active water treatment via reverse osmosis

If you wish to maintain a South American tank or a densely planted aquascape despite hard tap water, a reverse osmosis system is the most efficient solution. This technology has established itself as the gold standard in Swiss aquatics.

How does a reverse osmosis system work?

Tap water is forced under pressure through an extremely fine, semi-permeable membrane. This retains up to 98% of all dissolved substances – including calcium, nitrates and heavy metals. What remains is the so-called permeate, an almost pure water with a hardness of virtually 0° dH.

This pure water serves as the perfect base. By mixing it with normal tap water or adding specific mineral salts, you can precisely adjust the parameters to suit your fish. Modern systems are now extremely water-efficient and can be easily installed under any sink.

The alternative: adapting the fish stock to the water

However, technical treatment isn’t always necessary. An often underestimated strategy is to view existing Swiss tap water as an opportunity. There are fascinating fish species that really thrive in hard, alkaline water.

Specialists for hard water:

• Cichlids from East Africa: The inhabitants of Lake Tanganyika and Lake Malawi absolutely require hard water with high pH levels. Our Swiss water parameters are almost ideal for these colourful cichlids.
• Livebearing cyprinids: Classics such as guppies, platies and mollies are extremely hardy and prefer medium-hard to hard water.
• Rainbowfish: Many species from Australia display significantly better vitality and more intense colours in harder water.

Practical tips for stable operation

A critical factor in day-to-day care is evaporation. When water evaporates from the aquarium, the minerals remain in the tank. The result: the water gradually becomes harder. To counteract this effect, evaporated water should ideally always be topped up with pure osmosis water. This keeps the parameters constant – a crucial factor for the health of the fish.

Furthermore, CO2 fertilisation plays a dual role. In hard water, the pH value is usually high (above 7.5). A controlled supply of carbon dioxide not only nourishes the plants but also helps to bring the pH value into a more neutral range, which is essential for many aquatic plants to absorb nutrients.

Conscious management of water hardness is the foundation for a functioning ecosystem in the tank. Whether you opt for technical adjustments or specialise in species that thrive in our hard water – understanding your own water parameters is the first step towards success.

Here at AQUATANA, we support you in laying this foundation. In our aquatics shop, you’ll find everything you need to master your water parameters perfectly. Take your time to browse our online shop or let us advise you, so that your aquarium provides exactly the conditions your fish require.