Aquarium GH (General Hardness) Calculator

Enter your tank volume, current GH, and target GH to calculate the exact grams and tablespoons of Seachem Equilibrium (or equivalent) needed to reach your desired hardness level.

Created by Luis GonzalezLast updated: June 18, 2026

How to Use This Calculator

1
Enter Your Tank and GH Values
Input your tank volume in US gallons, your current GH reading in dGH (from a test kit), and your target GH level. Most community fish thrive between 6-12 dGH.
2
Review Results and Insights
The calculator displays the exact grams of Seachem Equilibrium needed, the GH increase, and approximate tablespoon and teaspoon measurements. The GH Test Result card shows where your current reading falls on the freshwater scale. The Insights panel shows mineral increase in ppm, standard doses required, and a target range assessment for your species.

Example Calculation

An aquarist with a 55-gallon tank measures their GH at 3 dGH and wants to raise it to a target of 8 dGH using Seachem Equilibrium.

Tank Volume (gal)

Current GH (dGH)

Target GH (dGH)

Results

Equilibrium Needed

91.1 g

GH Increase

5.0 dGH

Approximate Tablespoons

4.34 tbsp

Approximate Teaspoons

13.01 tsp

Tank Volume

208.2 L

Target GH Range

8 dGH

Insights card shows mineral ppm increase, standard doses needed, and target range assessment.

Tips

Dissolve Before Adding

Always pre-dissolve granular GH boosters like Seachem Equilibrium in a separate container of dechlorinated tank water before slowly adding it to your aquarium. This prevents localized mineral spikes that can stress fish and invertebrates.

Dose Gradually for Large Changes

For GH increases greater than 3-4 dGH (above roughly 50 ppm), split the calculated dose over 2-3 water changes across several days. The calculator's Insights panel flags large doses automatically.

Verify with a Test Kit

After dosing, re-test your GH after 12-24 hours to confirm the new level. Substrate, driftwood, and live plants can absorb minerals and shift readings slightly from the calculated target.

Match GH to Your Species

Use the Target GH Range card to confirm your target suits your fish. Discus and tetras prefer 3-6 dGH, community tanks do best at 6-12 dGH, and African cichlids thrive at 10-20 dGH.

Adjusting Your Aquarium's General Hardness for Species-Specific Needs

General Hardness (GH) is a crucial water parameter that measures the concentration of dissolved mineral ions like calcium and magnesium, essential for the health and osmoregulation of fish and invertebrates.

The Aquarium GH (General Hardness) Calculator provides precise dosing recommendations for products like Seachem Equilibrium to raise your tank's GH to an optimal level.

Most community fish thrive between 6-12 dGH, and achieving the correct GH is fundamental for preventing stress and promoting long-term well-being in your aquatic ecosystem in 2026.

The GH Adjustment Formula

The calculator determines the required amount of GH booster (e.g., Seachem Equilibrium) by first calculating the desired increase in GH, then scaling it based on the tank's volume.

The formula relies on the known properties of common GH-raising products.

liters = tank volume (gallons) x 3.78541
GH rise = target GH (dGH) - current GH (dGH)
grams Equilibrium = (GH rise / 3 dGH) x (liters / 80 L) x 21 grams
tablespoons = grams Equilibrium / 21 grams/tbsp
teaspoons = grams Equilibrium / 7 grams/tsp

Here, GH rise is the difference between your desired and current GH.

The constant 3 dGH and 80 L are based on the typical dosage recommendations for Seachem Equilibrium (21 grams, or 1 tablespoon, raises GH by 3 dGH in 80 liters of water).

💡 Accurate tank volume is critical for precise dosing. If you have an irregularly shaped tank, our Aquarium Volume Calculator (Bow Front) can help you determine its exact capacity.

Raising GH in a 55-Gallon Aquarium

Let's say an aquarist has a 55-gallon tank with a current GH of 3 dGH and wants to reach a target GH of 8 dGH.

Convert Tank Volume to Liters: liters = 55 gal x 3.78541 L/gal = 208.2 L.
Calculate Desired GH Increase: GH rise = 8 dGH - 3 dGH = 5 dGH.
Calculate Grams of Equilibrium Needed: grams Equilibrium = (5 dGH / 3 dGH) x (208.2 L / 80 L) x 21 g grams Equilibrium = 1.667 x 2.602 x 21 g = 91.1 g.
Calculate Approximate Tablespoons: tablespoons = 91.1 g / 21 g/tbsp = 4.34 tbsp.
Calculate Approximate Teaspoons: teaspoons = 91.1 g / 7 g/tsp = 13.01 tsp.

The calculator indicates approximately 91.1 grams of Seachem Equilibrium is needed, which is about 4.34 tablespoons or 13.01 teaspoons.

💡 For tanks with complex shapes, precise volume calculation for dosing remains essential. Our Aquarium Volume Calculator (Cylinder) can help determine volumes for round tanks.

The Importance of General Hardness for Aquatic Life

General hardness (GH) plays a pivotal role in the physiological processes of aquatic animals.

It directly influences osmoregulation, the vital process by which fish and invertebrates regulate the balance of water and salts within their bodies.

In water that is too soft (low GH), fish can struggle to maintain this balance, leading to stress, organ damage, and a compromised immune system.

Conversely, water that is excessively hard can also be detrimental to species adapted to softer conditions.

Maintaining the appropriate GH ensures robust health, vibrant coloration, and proper metabolic function.

Typical GH Requirements by Species

The ideal GH for an aquarium depends on the specific species being kept.

For sensitive soft-water species like Discus, Rummy Nose Tetras, or various dwarf cichlids, a GH range of 3-6 dGH (54-107 ppm) is recommended.

Most general community freshwater tanks thrive in moderately hard water at 6-12 dGH (107-214 ppm).

Species from hard water environments, such as livebearers (Mollies, Guppies) and African Rift Lake Cichlids, require 10-20 dGH (178-357 ppm) for optimal health and coloration.

Frequently Asked Questions

What is General Hardness (GH) in an aquarium?

General Hardness (GH) measures the concentration of dissolved divalent metal ions, primarily calcium (Ca2+) and magnesium (Mg2+), in aquarium water. It is expressed in degrees of hardness (dGH), where 1 dGH equals approximately 17.848 ppm of dissolved minerals. These minerals are essential for fish osmoregulation, bone development, and enzyme function.

Why is GH important for fish health?

Calcium and magnesium ions regulate osmoregulation, the process by which fish balance salt and water in their bodies. Insufficient GH leads to osmotic stress, organ damage, and weakened immunity. Excessive GH stresses soft-water species. Matching GH to your species' natural habitat is one of the most impactful things you can do for long-term fish health.

What is Seachem Equilibrium, and how does it raise GH?

Seachem Equilibrium is a mineral salt blend designed to re-mineralize RO/DI water or raise GH in freshwater aquariums. One tablespoon (21 g) raises GH by 3 dGH in 80 liters of water. It adds calcium, magnesium, and potassium without significantly affecting KH or pH, making it safe for planted tanks.

Can I use a different GH booster with this calculator?

Yes, but you may need to adjust the dose. This calculator is calibrated for Seachem Equilibrium (21 g per 3 dGH per 80 L). Other products like Salty Shrimp GH+ or DIY calcium sulfate/magnesium sulfate blends have different dosing rates. Check your product's label and scale accordingly.

How often should I re-dose after water changes?

Every water change dilutes your GH. If you replace 25% of the water with RO or soft tap water, your GH drops by roughly 25%. Re-test after each water change and use the calculator with your new current GH to determine the top-up dose needed.

Can GH levels be too high for aquarium fish?

Yes. Excessively high GH stresses species adapted to soft water, such as Discus, Cardinal Tetras, and many dwarf cichlids. Very hard water can also impair plant nutrient uptake. If your GH exceeds your species' recommended range, dilute with RO or distilled water rather than adding more minerals.