GH in Aquarium: How to Raise GH and KH in My Tank?

Most freshwater aquariums do well with GH and KH between 4-8 degrees (70-140 ppm). However, some fish genuinely need harder water. Livebearers, goldfish, and African cichlids are natural hard-water lovers. If your tap water is already fairly hard, you may simply need to maintain it with regular water changes. But if you're starting with soft water-or if you're seeing signs like lethargy in your fish, melting aquarium plants, or thin, flaking snail shells-then raising GH and KH becomes necessary.

Testing Your Current GH and KH Levels

You cannot raise GH and KH effectively without knowing where you're starting from, so testing is the first step.

Using Test Kits and Strips

API GH/KH Test Kit (liquid reagent):

• Fill a test tube to the 5 mL line with aquarium water.

• For KH: Add one drop of KH reagent and invert several times. Keep adding drops (counting as you go) until the color changes from blue to yellow. The number of drops equals your KH in degrees.
• For GH: Use the GH bottle instead, adding drops until the color shifts from orange to green.
• Both kits include conversion charts to convert degrees to ppm if you prefer that unit.

Tetra 6-in-1 Test Strips:

• Dip the strip in your aquarium water for one second and lay it flat.
• After 30-60 seconds, compare the color blocks on the back of the jar to read GH and KH.

• These strips are convenient and economical (you can even cut them in half for twice the uses).

Test at least once a month as preventative maintenance. Many hobbyists find that regular testing helps them catch imbalances before they cause fish or plant problems.

How to Raise GH and KH: Proven Methods

Using Crushed Coral (Most Effective)

Crushed coral is the classic, most affordable way to raise both GH and KH simultaneously. The calcium carbonate in the coral dissolves slowly in your water, releasing minerals and buffering capacity over time.

How to use crushed coral:

• Add 1 pound of crushed coral per 10 gallons of tank water.
• Place it directly in your substrate, or (if you prefer not to see it) pack it into a mesh media bag and position it in your filter-canister, hang-on-back, or internal.
• The lower your starting pH, the faster the coral dissolves. You may need to replace it every 6-12 months depending on how acidic your water is.

• Test your water every month to monitor progress and know when to add more.

The main drawback: if you prefer a clean substrate aesthetic or have a non-customizable filter, the coral may not fit your setup.

Using Equilibrium or Similar Mineralizers

If crushed coral doesn't suit your tank design, Seachem Equilibrium and similar products offer a gentler, more precise alternative. These are dry salt mixes that you dissolve in water before adding to your tank.

How to use Equilibrium:

• Follow the package dosing instructions (typically 1 teaspoon per 5 gallons raises GH by 1-2 degrees).
• Dissolve the powder in a cup of tank water first, then pour it into the aquarium.
• Dose gradually and retest after a few days before adding more.
• This method gives you finer control but requires more frequent dosing than crushed coral.

Using Wonder Shells

Wonder Shells are calcium-based tablets designed to slowly dissolve and release minerals. They're convenient for smaller tanks or if you want a "set it and mostly forget it" approach.

How to use Wonder Shells:

• Drop one shell into your filter or substrate.
• They dissolve gradually, raising GH and KH over weeks.
• Replace when fully dissolved (typically every 4-6 weeks, depending on tank size and water chemistry).

Increasing Water Changes (If Your Tap Water Is Already Hard)

If your tap water is naturally hard (which you can check by testing it separately), you may not need supplements at all. Simply doing more frequent water changes can maintain your GH and KH. This is the gentlest approach if it applies to your situation.

When and Why You Need to Raise GH and KH

Signs Your Tank Needs Higher GH and KH

• Aquarium plants melting or struggling to grow, even with fertilizer dosed correctly. Low mineral levels starve plants of calcium and magnesium.
• Fish showing lethargy, slow growth, or faded coloration. Minerals are essential for osmoregulation and healthy metabolism.
• Shrimp dying during molting. They need sufficient calcium and magnesium to harden their new exoskeleton.
• Snail shells appearing thin, flaky, or developing holes. This is a classic sign of calcium deficiency.
• pH crashing or swinging wildly between water changes. Low KH means your buffer capacity is exhausted.

Species That Prefer Hard Water

If you're keeping any of these fish or invertebrates, maintaining adequate GH and KH is non-negotiable:

• Livebearers (guppies, mollies, platies)
• Goldfish
• African cichlids
• Corydoras catfish (benefit from moderate hardness)

Measuring What's Actually in Your GH

One important caveat: GH measures both calcium and magnesium ions together. It's theoretically possible to have a high GH reading that's mostly magnesium with little calcium-leaving your plants and snails deficient.

If you suspect this is happening (for example, your plants still struggle despite high GH), consider purchasing a calcium-specific test kit to see the breakdown. Most general aquarium shops stock these, though they're less commonly needed than GH and KH tests. For most hobbyists raising GH with crushed coral or Equilibrium, the ratio is close enough to healthy.

Practical Maintenance Schedule

To keep your water chemistry stable and avoid the problems that motivated this article in the first place:

• Test GH and KH at least once a month as preventative maintenance.
• Log your results in a simple spreadsheet or notebook to spot trends.
• Replace crushed coral or Wonder Shells on schedule (every 6-12 months, depending on your setup).
• Perform regular water changes (25-50% every 1-2 weeks) to maintain fresh minerals and prevent salt creep.
• If you switch to RO/DI water (reverse osmosis deionized water, used to lower hardness), you'll need to remineralize it using Equilibrium or similar, which gives you precise control.

Common Mistakes to Avoid

• Not testing before and after raising GH/KH. You might overshoot and cause problems for soft-water species.
• Using boiling or distilling tap water to soften it, then forgetting to remineralize. Pure water lacks the minerals your fish and plants need.
• Dosing crushed coral or Equilibrium all at once. Gradual, monitored increases are safer and less likely to shock your tank.
• Ignoring pH alongside GH and KH. These parameters are connected; raising KH often raises pH, which may affect your fish depending on species.

The Bottom Line

Raising GH and KH is straightforward once you know your starting point. Test your water, choose a method that fits your setup, and dose gradually while monitoring. Your plants will grow vigorously, your fish will stay healthy, your shrimp will molt successfully, and your snails will develop strong shells-all because you took the time to understand and adjust your aquarium's mineral balance.