How to Harden Aquarium Water for Livebearers and Cichlids

Table of Contents

• Why You Might Need to Harden Your Aquarium Water
• Singapore Tap Water: Soft by Default
• Species That Need Harder Water
• Methods to Harden Aquarium Water
• Dosing to Target GH
• Monitoring and Maintaining Hardness
• Frequently Asked Questions

Why You Might Need to Harden Your Aquarium Water

While much of the fishkeeping hobby focuses on softening water for South American and Southeast Asian species, there is a significant group of popular aquarium fish and invertebrates that actually require harder water than what comes out of the tap in many regions. These species evolved in mineral-rich environments — the alkaline rift lakes of Africa, the limestone springs of Central America, and hard-water rivers where dissolved calcium and magnesium are abundant.

For these animals, soft water is not just suboptimal — it can cause genuine health problems. Livebearers struggle to maintain proper osmoregulation in very soft water. Snails cannot build and maintain their shells without adequate calcium. African cichlids become stressed and disease-prone when kept in conditions far removed from their natural water chemistry.

Singapore Tap Water: Soft by Default

Singapore’s PUB-treated tap water is naturally soft, typically testing at:

• GH: 2 to 4 dGH
• KH: 1 to 3 dKH
• pH: 7.0 to 8.0

For many tropical community species, this softness is fine or even ideal. But for species that require GH of 8 dGH or higher, Singapore tap water is genuinely deficient. Livebearers kept in straight tap water may survive, but they will not thrive. Snail shells may thin and erode. African cichlids may exhibit stress behaviours and reduced coloration.

The good news is that hardening water is straightforward, inexpensive, and can be achieved through several reliable methods.

Species That Need Harder Water

For a comprehensive understanding of GH, KH, and how they interact with pH, see our GH and KH aquarium guide.

Methods to Harden Aquarium Water

Crushed Coral

Crushed coral (calcium carbonate) is the most popular passive method for hardening aquarium water. It dissolves slowly, raising both GH and KH simultaneously. The rate of dissolution is self-regulating — it dissolves faster in softer, more acidic water and slower as hardness and pH increase.

How to use:

• Place in a mesh bag inside your filter canister or hang-on-back filter for consistent dissolution
• Alternatively, mix into the substrate (common in African cichlid tanks)
• Start with 100 to 200 grams per 100 litres and adjust based on test results after one week
• Replace every 3 to 6 months as the coral dissolves and loses effectiveness

Pros: Inexpensive, low-maintenance, self-regulating, widely available.

Cons: Cannot precisely target a specific GH independently from KH. Raises both together.

Seiryu Stone and Limestone

Seiryu stone, limestone, and other calcium carbonate-based rocks gradually harden water as they dissolve. The effect is slower and less controllable than crushed coral in the filter because the surface area exposed to water is proportionally smaller. However, these rocks serve a dual purpose — they harden the water while also providing attractive hardscape for aquascaping.

In an African cichlid setup, limestone rockwork creates a naturalistic environment that simultaneously maintains the water chemistry these fish need. Seiryu stone is popular in planted tanks but can push GH and KH higher than desired for soft-water species — for cichlid and livebearer tanks, this is a feature rather than a problem.

Seachem Equilibrium

Seachem Equilibrium is a commercial remineraliser designed specifically for planted aquariums. It raises GH without significantly affecting KH or pH, making it useful when you need to add calcium, magnesium, and potassium without altering your tank’s alkalinity.

How to use:

• Dose according to the manufacturer’s instructions (approximately 1 tablespoon per 80 litres raises GH by about 3 dGH)
• Dissolve in water change water before adding to the tank
• Re-dose with each water change to maintain target GH

Pros: Precise dosing, raises GH independently of KH, includes beneficial plant nutrients (potassium, iron, manganese).

Cons: Ongoing cost, requires dosing with every water change, not a set-and-forget solution.

GH and KH Remineralisers

Products such as SaltyShrimp GH/KH+ and Salty Shrimp Mineral GH/KH are formulated to raise both GH and KH in a controlled, measurable way. They are widely used by shrimp keepers who mix remineraliser into RO water, but they work equally well for hardening tap water for livebearers and cichlids.

How to use:

• Add remineraliser to a bucket of water and stir until dissolved
• Test the GH and KH of the prepared water
• Adjust the dose until the prepared water matches your target
• Use this prepared water for all water changes

This method offers the most precise control, as you can dial in exact GH and KH values. It requires a bit more effort per water change but produces highly consistent results.

Cuttlebone

Cuttlebone — the internal shell of the cuttlefish — is composed of aragonite (a form of calcium carbonate). Placing a piece in the tank slowly releases calcium, raising GH and KH. It is inexpensive, readily available from pet shops (typically sold for birds), and lasts several weeks to months depending on water acidity.

Cuttlebone is a practical calcium supplement for snail tanks in particular. It is a less precise method than commercial remineralisers but works well as a low-maintenance calcium source.

Dosing to Target GH

The key to hardening aquarium water successfully is knowing your starting point and your target, then adjusting gradually.

1. Test your tap water’s GH and KH. This is your baseline. In Singapore, expect GH 2 to 4 and KH 1 to 3.
2. Determine your target. For guppies and platies, aim for GH 8 to 12. For African cichlids, GH 12 to 18. For mystery snails, GH 8 to 15.
3. Choose your method. For a passive, low-maintenance approach, use crushed coral in the filter. For precise control, use a commercial remineraliser.
4. Adjust gradually. Increase GH by no more than 2 to 3 dGH per day to avoid shocking your fish. If using crushed coral, the gradual dissolution naturally limits the rate of change. If using remineralisers, mix your target water in a bucket and replace tank water gradually through water changes.
5. Verify with testing. Test GH and KH 24 to 48 hours after any adjustment. Confirm stability over a week before considering the target achieved.

Monitoring and Maintaining Hardness

• Test GH and KH weekly, at minimum during the initial setup period. Once stable, biweekly testing is sufficient.
• Re-dose remineralisers with every water change. Fresh tap water in Singapore is soft; adding it without remineralisation dilutes the hardness you have built up. Always prepare your water change water to match the tank’s target GH and KH before adding it.
• Monitor crushed coral levels. As coral dissolves, its effectiveness diminishes. Top up or replace the coral in your filter when you notice GH starting to drift downward.
• Watch for signs of mineral deficiency in livestock. Snails with pitting, white erosion, or thin shells need more calcium. Shrimp with moulting difficulties may need higher GH. Livebearers that seem lethargic or prone to disease in soft water often improve markedly when GH is raised to their preferred range.

Frequently Asked Questions

Can I just add calcium chloride to raise GH?

Calcium chloride raises GH (it adds calcium) without affecting KH. It is used in some DIY remineraliser recipes alongside magnesium sulphate (Epsom salt) and baking soda. However, dosing individual chemicals requires careful calculation and testing to avoid imbalances. For most hobbyists, a commercial remineraliser is simpler, more balanced, and less risky. If you do use calcium chloride, add it in small increments and test GH after each addition.

Will hardening the water affect my plants?

Most aquarium plants tolerate a broad range of GH (2 to 15 dGH) without issues. Some plants that prefer very soft water — such as Tonina and certain rare stem plants — may struggle above GH 8 to 10. Common species like Java fern, Anubias, Cryptocoryne, Vallisneria, and Amazon sword grow well in moderately hard water. Vallisneria, in fact, prefers harder water and does poorly in very soft conditions.

My snails’ shells are eroding. How quickly will hardening the water help?

Existing shell damage cannot be reversed — calcium carbonate shell that has dissolved away is gone permanently. However, raising GH to 8 dGH or higher stops further erosion and allows the snail to grow new, healthy shell material. You should see improvement in new growth within 2 to 4 weeks. Adding a cuttlebone or crushed coral directly to the tank provides an additional calcium source that snails can rasp on directly.

Is Epsom salt (magnesium sulphate) a good way to raise GH?

Epsom salt raises GH by adding magnesium, but it does not add calcium. Since most species that need hard water require both calcium and magnesium, Epsom salt alone is insufficient. It is useful as part of a balanced remineralisation approach (calcium chloride for calcium, Epsom salt for magnesium) but not as a standalone solution. It also has a mild laxative effect on fish at higher doses, which can be therapeutic for constipation but is undesirable as a permanent water additive at elevated concentrations.

Give Your Hard-Water Species What They Need

Singapore’s naturally soft tap water is excellent for many tropical species, but it falls short for livebearers, African cichlids, and snails that depend on dissolved minerals for health, coloration, and shell integrity. Hardening your water is simple — crushed coral in the filter handles most situations, and commercial remineralisers provide precision when you need it.

For crushed coral, Seiryu stone, remineralisers, cuttlebone, and expert advice on water chemistry for your specific setup, visit Gensou at 5 Everton Park, Singapore. Our team has been helping hobbyists dial in their water parameters for over 20 years — whether you are setting up your first livebearer tank or fine-tuning a Tanganyikan cichlid display.

Related Reading

• How to Harden Soft Water for Livebearers and African Cichlids
• Aquarium Cloudy After Water Change: Why and How to Fix It
• How Often to Change Aquarium Water: Finding Your Schedule
• Water Change Temperature Matching: Why It Matters
• Aquarium Water Conditioners Explained: Prime, Safe and Beyond