Understanding GH: Why General Hardness Matters in Axolotl Tanks

When caring for axolotls, most people quickly learn about ammonia, nitrite, nitrate, pH, and temperature.

But there is another important water parameter that often gets overlooked:

GH, also known as General Hardness.

GH plays an important role in your axolotl’s overall health, mineral balance, gill condition, growth, and comfort. It may sound technical at first, but once you understand what GH does, it becomes much easier to manage.

This guide explains what GH is, why it matters for axolotls, how to test it, and what to do if your GH is too low or too high.

What Is GH?

GH stands for General Hardness.

It measures the amount of dissolved minerals in your aquarium water, mainly:

• Calcium

• Magnesium

These minerals are naturally found in water and are important for aquatic animals.

In simple terms, GH tells you whether your water is soft or hard.

Soft water has fewer dissolved minerals.

Hard water has more dissolved minerals.

Axolotls generally do best in moderately hard water because they need minerals to support healthy body function, skin, gills, bones, and development.

Why GH Matters for Axolotls

Axolotls absorb minerals from their environment as well as from their food.

Because they live fully aquatic lives, the water around them directly affects their health.

Correct GH helps support:

• Healthy gill function

• Strong growth

• Normal mineral balance

• Good skin condition

• Healthy bones and body structure

• Stable long-term wellbeing

• Comfortable water conditions

If GH is too low, the water may not provide enough essential minerals.

If GH is too high, the water may become overly mineral-rich and potentially uncomfortable.

Like most axolotl care, the goal is balance.

Little Lotl’s Recommended GH Range

For axolotls, Little Lotl’s recommends:

GH: 7 to 14 dGH

This range provides a healthy level of dissolved minerals without making the water excessively hard.

The full recommended axolotl water parameters are:

Temperature: 14°C to 18°C (57°F to 64°F)

pH: 7.2 to 8.2

Ammonia: 0 ppm

Nitrite: 0 ppm

Nitrate: Less than 20 ppm

GH: 7 to 14 dGH

KH: 4 to 8 dKH

GH should always be considered alongside the other parameters, especially pH and KH.

GH vs KH: What Is the Difference?

GH and KH are often confused, but they are not the same thing.

GH: General Hardness

GH measures dissolved minerals, mainly calcium and magnesium.

It affects mineral availability and overall water hardness.

KH: Carbonate Hardness

KH measures carbonate and bicarbonate levels.

It helps buffer pH and keep the aquarium stable.

Put simply:

GH = mineral content

KH = pH stability

Both are important, but they do different jobs.

A tank can have low GH and high KH, or high GH and low KH, depending on the water source and products used.

How Do You Test GH?

GH is usually tested with a liquid GH test kit.

The test commonly works by adding drops to a water sample until the colour changes.

Each drop usually represents one degree of hardness, known as dGH.

For example:

• 4 drops = 4 dGH

• 8 drops = 8 dGH

• 12 drops = 12 dGH

Always follow the instructions on your specific test kit.

Testing GH is especially useful if:

• You use rainwater, RO water, or very soft tap water

• Your axolotl has ongoing gill or skin concerns

• You are cycling a new tank

• You are moving house

• Your tap water source changes

• You are adjusting water minerals

• You keep snails, shrimp, or live plants as well

Signs GH May Be Too Low

Low GH means the water does not contain enough dissolved minerals.

Possible signs of low GH problems may include:

• Poor gill condition

• Reduced growth in juveniles

• Soft or unstable water chemistry

• Difficulty maintaining healthy mineral balance

• Increased sensitivity to water changes

• General stress

• Poor condition in snails or shrimp if kept separately in suitable setups

Low GH is common in some areas with naturally soft tap water.

If GH is too low, your axolotl may not be getting the mineral support it needs from the water.

Signs GH May Be Too High

High GH means the water contains a large amount of dissolved minerals.

Axolotls can tolerate moderately hard water, but very high GH may be less comfortable.

Possible issues with very high GH may include:

• Mineral deposits on glass or equipment

• Difficulty adjusting other water parameters

• Increased hardness beyond the ideal range

• Stress if changes happen suddenly

The biggest concern is not usually a slightly high GH. Sudden changes are often more stressful than a stable reading just outside the ideal range.

Stability matters.

Axolotls are not fans of surprise chemistry.

What Causes Low GH?

GH may be low if your water source contains very few minerals.

Common causes include:

• Naturally soft tap water

• Rainwater use

• Reverse osmosis water

• Distilled water

• Heavy dilution with low-mineral water

• Some water sources in soft-water regions

If you use RO, rainwater, or distilled water, it must be remineralised before being used for axolotls.

Plain RO or distilled water is not suitable on its own because it lacks essential minerals.

What Causes High GH?

GH may be high if your water source is naturally mineral-rich.

Common causes include:

• Hard tap water

• Limestone-based rocks

• Crushed coral

• Shell grit

• Mineral additives

• Evaporation concentrating minerals

• Some substrates or décor

If water evaporates, minerals stay behind. Topping up evaporation without water changes can slowly increase hardness over time.

Regular water changes help keep minerals balanced.

How to Raise GH Safely

If GH is too low, raise it slowly.

Safe ways to increase GH may include:

• Using an axolotl-safe GH mineral supplement

• Using remineralised water

• Adding minerals gradually during water changes

• Testing regularly while adjusting

Do not make sudden large changes.

Raise GH slowly over time so your axolotl can adjust comfortably.

When using a GH supplement, follow the product directions carefully and test before and after dosing.

How to Lower GH Safely

If GH is too high, lower it slowly.

This may be done by gradually mixing in lower-GH water, such as properly prepared RO water, during water changes.

Important:

• Never use plain RO or distilled water without remineralising appropriately

• Avoid sudden swings

• Test regularly

• Adjust gradually

• Keep pH and KH stable

Large sudden drops in GH can stress your axolotl.

A slow adjustment is much safer than a dramatic one.

Can You Use Bottled Water for Axolotls?

Bottled water is not automatically safe or suitable.

Some bottled water has very low minerals. Some has high minerals. Some may affect pH, GH, or KH.

Before using bottled water, test it for:

• pH

• GH

• KH

• Ammonia

• Nitrite

• Nitrate

Conditioned tap water is usually easier and more consistent for most keepers, provided it falls within suitable ranges or can be adjusted safely.

Does GH Affect pH?

GH and pH are connected but not the same.

GH measures minerals.

pH measures acidity or alkalinity.

KH has a stronger role in stabilising pH, but GH can still be part of the overall water chemistry picture.

This is why it is helpful to test GH, KH, and pH together rather than looking at only one number.

GH and Live Plants

Some aquarium plants do better when minerals are available in the water.

Very soft water may limit plant growth, depending on the species.

Hardy beginner plants such as Java fern, Anubias, Elodea, Hornwort, Java moss, Vallisneria, Amazon sword, Subwassertang, and floating plants can often do well in axolotl-safe conditions, but stable water is still important.

Plants are lovely little water-roommates, but axolotl safety always comes first.

GH and Tank Cycling

Beneficial bacteria need stable conditions to thrive.

GH is not the only factor in cycling, but overall mineral balance can support a stable aquarium environment.

For cycling, you should monitor:

• Ammonia

• Nitrite

• Nitrate

• pH

• KH

• GH

• Temperature

If your water is very soft, low KH and low GH may contribute to unstable conditions.

This is why testing GH and KH can help when a tank seems stuck or unpredictable.

Should You Chase a Perfect GH Number?

No.

Do not chase perfect numbers every day.

The goal is a safe, stable range.

For axolotls, aim for 7 to 14 dGH, but avoid constantly adjusting the tank unless there is a clear issue.

Constant chemical changes can stress axolotls more than a stable reading that is only slightly outside ideal.

Test, understand the trend, and adjust slowly if needed.

Common GH Mistakes to Avoid

Avoid these common GH problems:

• Never testing GH

• Using RO or distilled water without minerals

• Raising GH too quickly

• Lowering GH too quickly

• Confusing GH with KH

• Assuming clear water means correct minerals

• Adding random rocks or shells without testing

• Overusing mineral products

• Forgetting that evaporation can concentrate minerals

GH is not scary once you know what it means.

It is just another piece of the water-quality puzzle.

Little Lotl’s GH Checklist

For healthy axolotl water:

• Test GH with a reliable kit

• Aim for 7 to 14 dGH

• Keep changes gradual

• Test KH and pH as well

• Avoid plain RO or distilled water

• Use axolotl-safe products only

• Keep water cool and clean

• Watch your axolotl’s behaviour and gill condition

• Do regular water changes

Final Thoughts

GH is an important part of axolotl water care.

It tells you how much calcium and magnesium are available in the water and helps you understand whether your tank water is too soft, too hard, or just right.

For axolotls, a GH range of 7 to 14 dGH is a great target.

When GH is stable, your axolotl has better mineral support, healthier water conditions, and a more comfortable environment.

As always, the best care comes back to the basics:

Clean water. Cool temperatures. Stable parameters. Regular testing.

Get those right, and your little lotl has a much better chance of thriving.