How to Soften Hard Water for Sensitive Fish

No, hard water isn’t another name for ice.

In aquariums, water hardness refers to the concentration of minerals found in the water. So how can anyone tell if water is hard? 

Typically, a water hardness test kit is used to measure GH (General Hardness) and KH (Carbonate Hardness).

If the GH level is above 12° dGH or the KH level is high (generally above 18°), your water is considered hard. 

Many delicate fish species prefer softer water, so adjusting these parameters can make all the difference.

If you’re dealing with hard water for your sensitive fish, this blog will walk you through various methods of softening it.

How to Test Water Hardness

Testing your water’s GH and KH is easy and essential for keeping your aquarium balanced. You can use test kits available at pet stores, which usually come with clear instructions.

Simply follow the steps of the package.

Usually they go something like this: add a few drops of the testing solution to a water sample, and compare the color change to the provided chart.

Aim to test weekly, especially when you're just starting out or making changes to your tank.

​​Water Hardness Scale

Here's a quick rundown of water hardness levels for freshwater aquariums:

• Very Soft: 0-3 dGH (0-50 ppm)
• Soft: 3-6 dGH (50-100 ppm)
• Medium Hard: 6-12 dGH (100-200 ppm)
• Hard: 12-18 dGH (200-300 ppm)
• Very Hard: 18+ dGH (300+ ppm)

Most reasonably sensitive fish species, like Ember Tetras, Celestial Pearl Danios, and Chili Rasboras, prefer soft to very soft water. Anything above 12 dGH (degree of GH) is generally considered hard water.

Methods to Soften Hard Water

If you’re dealing with hard water, don’t worry—there are several effective ways to soften it and create a more comfortable environment for your sensitive fish. Let’s look at some of the most popular methods.

Peat Moss

When you add it to your aquarium, it releases tannins and acids, which help lower both GH and KH. To use peat moss, you can place it directly in your filter or inside a mesh bag submerged in the tank.

Before adding it, soak the peat in water for a few days to remove any excess debris and prevent cloudiness.

However, keep in mind that peat moss may slightly lower the pH and tint the water a tea-like color, which some aquarists find less appealing.

It's perfect of you're going for a true-to-nature biotope though!

Driftwood

Driftwood works similarly to peat moss by releasing tannins that gradually reduce GH and KH. It also adds a rustic, natural look to your aquarium.

To prepare driftwood, soak it in water for a few days or even weeks to allow the tannins to leach out and avoid a sudden drop in water hardness. Be aware that driftwood can also darken the water, giving it a brownish hue.

This color is harmless and often mimics the fish’s natural habitat, but if you prefer clearer water, it might not be for you.

Indian Almond Leaves

When added to the tank, Indian almond leaves release tannins that help lower both GH and KH, similar to peat moss and driftwood.

These leaves also have additional benefits, such as promoting healthy conditions for sensitive species by mimicking their natural, soft-water habitat. It’s also said to provide anti-fungal and anti-bacterial properties.

Like driftwood and peat moss, Indian almond leaves can also tint the water a brownish color.

Now, adding botanicals to soften the water is really only going to budge you a couple degrees of hardness. Even less if you do water changes often.

For serious hobbyists (with more skill), try using soft water at the start: Reverse Osmosis.

Reverse Osmosis (RO)

The RO process involves pushing water through a semi-permeable membrane, which removes most of the minerals, resulting in very soft water with minimal GH and KH.

This method is ideal for aquarists who need precise control over water parameters.

However, because RO water is almost entirely stripped of minerals, remineralization is needed to ensure your fish still gets the essential nutrients they need.

You can do this by adding a remineralization product specifically designed for aquariums.

Many people have these basic three-stage RO systems in their house (often under the kitchen sink). They provide clean drinking water when the household's tap or well water is undesirable for whatever reason. 

If you don't feel like spending the $300+ to get a system installed in your home, you may be able to buy reverse osmosis water at the grocery store or your local fish place.

Grocery stores have these water kiosks in the beverage aisle that retail a gallon of RO water for under $1 here in the midwest.

Other Methods to Soften Water

Water conditioners and ion exchange resins offer quick solutions for softening aquarium water. Some conditioners specifically target hardness, binding to calcium and magnesium ions.

They're easy to use—just add the recommended dose during water changes.

Ion exchange resins work by swapping hardness ions for sodium ions. You can use them in your filter or in a separate container to treat water before adding it to your tank.

While effective, these methods require careful dosing to avoid sudden parameter shifts.

They're great options if you need a quick fix. But natural methods like peat moss or driftwood often provide more stable, natural, cost- effective, and long-term results.

Additional Tips

• Combine Methods for Optimal Results: Mixing different methods, like using driftwood with reverse osmosis water, can help achieve softer water more effectively.
• Monitor Water Parameters Regularly: Keep a close eye on GH, KH, and pH levels weekly to ensure your aquarium stays stable and safe for your fish.
• Gradual Water Changes: Make water changes slowly to avoid stressing your fish, allowing them time to adjust to softer water.
• Importance of Water Stability: Once you reach the desired water softness, focus on maintaining consistent conditions to keep your fish healthy and stress-free.

Takeaway

Softening hard water isn't that difficult, but it does take some know-how and patience.

Have a look at these options and see what makes the most sense for your fish, your budget, and the kind of lifestyle you want to have when it comes to your fishkeeping. 

Are you more hands- off? Do you prefer your parameters absolutely exact, and your routine flawless?

It may be worth thinking about the fish you'd like to keep. Perhaps the water in your area is never going to be soft enough to keep some species.