GH, KH, and TDS: The Three Water Numbers That Confuse Everyone

In Part 1 of this water series, I talked about soft vs hard water in simple language – like soup with more or less “ingredients” inside.

Now we’re going to meet the three “famous” characters behind that softness and hardness:

• GH

• KH

• TDS

These three can look very scary on charts and forums.
People say things like:

“My GH is 6, KH 2, TDS 170, pH 6.5 – is this okay?”

If you’re new, it feels like reading some secret code.

In this post, I want to explain:

• What GH, KH, and TDS actually mean

• Why shrimp and plants care about them

• How they connect to soft vs hard water

• How to think about them without panic

This is not a lab manual. It’s just one hobbyist trying to keep shrimp and plants alive using real-world water.

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1. Quick Recap: Soft vs Hard Water (From Part 1)

From Part 1:

• Soft water = fewer dissolved minerals

• Hard water = more dissolved minerals

We used the “soup” example:

• Soft water → like light, clear soup

• Hard water → like soup with lots of invisible ingredients (minerals)

GH, KH, and TDS are just ways to measure pieces of that “soup”.

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2. GH – General Hardness

“How much mineral soup do we have?”

GH (General Hardness) measures mainly calcium and magnesium in the water.

These are important for:

• Shrimp shells

• Fish bones

• Plant structure and growth

You can imagine GH as:

“How much mineral ‘meat’ is inside the water?”

Higher GH → more minerals.
Lower GH → fewer minerals.

Why shrimp care:

• Shrimp need calcium and other minerals to:

  • Build and harden their shell

  • Molt properly

  • Recover after molting

If GH is too low (very soft water):

• Shells can be weaker

• Molting problems may occur

• Shrimp may be more delicate

If GH is moderate:

• Often ideal for common shrimp like Neocaridina

• Enough minerals for healthy shells, not too extreme

If GH is very high:

• Some hardy shrimp still live in it

• But sensitive types can struggle

• You might see more crust (limescale) on glass and equipment

We don’t need exact numbers in this post. The important idea:

GH = mineral level.
Shrimp and plants need some, not zero.

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3. KH – Carbonate Hardness

“The bodyguard that protects your pH”

If GH is about minerals for shell and bones, KH (Carbonate Hardness) is about stability.

KH measures how much carbonate and bicarbonate is in the water – these act like a buffer.

You can think of KH as:

“The bodyguard that keeps pH from mood swings.”

• Low KH = pH can change easily

  • Good if you want softer, more acidic water

  • But dangerous if you don’t understand it, because pH can crash quickly

• Medium KH = pH is more stable

  • Good for beginners and many community tanks

  • pH doesn’t jump around with every little thing

• High KH = pH fights back when you try to change it

  • Harder to lower pH

  • Water stays more alkaline (higher pH)

Why KH matters in our tanks:

• If KH is almost zero and we keep adding organic stuff (soil, leaves, heavy feeding), pH can slowly slide down and then suddenly drop → this is called a pH crash.

• If KH is very high, it’s very hard to lower pH without doing something drastic – and big sudden changes can stress shrimp and fish.

So KH is not “good” or “bad” by itself. It’s more like:

“How strong is my water’s pH shield?”

For most beginner shrimp and planted tanks, a moderate KH is easier to live with than ultra-low or ultra-high extremes.

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4. TDS – Total Dissolved Solids

“How much stuff is dissolved in total?”

TDS (Total Dissolved Solids) tells you, very roughly:

“How much ‘stuff’ is dissolved in the water altogether?”

This includes:

• Minerals (calcium, magnesium, etc.)

• Salts

• Nutrients

• Even some organic waste

Shrimp keepers often use a little TDS pen because:

• It’s cheap

• It’s fast

• It gives a quick “snapshot” of how loaded the water is

But TDS is not a direct measurement of water quality.
A high TDS could mean:

• Good minerals (from your shrimp salts), or

• A lot of waste and leftover food, or

• A mix of both

So TDS is like:

“The weight of everything dissolved,”
but it doesn’t tell you what exactly is in there.

It’s still useful because:

• If you mix water the same way every time, a TDS pen helps you repeat that mix.

• Sudden big changes in TDS (for example after a water change) can shock shrimp.

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5. How GH, KH, TDS, and Soft/Hard Water Fit Together

Let’s connect them in a simple picture.

• GH = minerals for shells, bones, and some plant needs

• KH = pH bodyguard (buffer)

• TDS = total amount of dissolved stuff (minerals + everything else)

• Soft vs Hard = more or less minerals in general

A few typical situations:

1. Soft water

   • GH: low

   • KH: often low

   • TDS: low

   • pH: can be more acidic and less stable if KH is very low

2. Moderately hard water

   • GH: medium

   • KH: medium

   • TDS: medium

   • pH: often around neutral to slightly alkaline, fairly stable

3. Very hard water

   • GH: high

   • KH: high

   • TDS: high

   • pH: often alkaline and very stubborn to change

These are just patterns, not strict rules.
Real tap water can be weird sometimes.

The main thing is:

When GH and KH are very low → be careful of pH swings.
When GH and KH are very high → water is stable, but harder to “soften”.

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6. Do I Need to Buy Test Kits Right Now?

If your budget is limited, or it’s hard to find test kits where you live, here’s my honest opinion:

• You can start with just:

• A basic dechlorinator (to remove chlorine/chloramine)

• Stable routines (temperature, water changes)

• Choosing hardy shrimp and plants that can live in typical tap water

Later, if you want to go deeper, useful tools are:

• A GH/KH drop test kit

  • You add drops until water changes color and count the drops.

  • Gives you a rough idea of GH and KH.

• A TDS pen

  • Dip, read the number.

  • Great for consistency when mixing water, especially if you ever use RO + remineralizer in the future.

These tools are helpful, but they are not magic.
They don’t replace:

• Good maintenance

• Not overfeeding

• Not overcrowding

• Being patient

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7. “What Numbers Should I Aim For?”

This is the part where the internet loves to argue.
Every species, breeder, and region has their own “perfect” range.

Here, I’ll keep it gentle and general:

For beginner-friendly Neocaridina shrimp, many people successfully keep them in:

• Low to medium GH and KH, using regular tap water

• Medium TDS, not super low, not extremely high

• Most important: no sudden changes

Instead of chasing exact numbers immediately, you can:

1. Find out roughly if your tap water is soft / medium / hard.

2. Choose livestock that matches that reality.

3. Keep conditions stable.

Later, when you have GH/KH tests and a TDS pen, you can:

• Measure your tap water

• Measure your tank water

• Learn what numbers you’ve been using all along

You might discover: “Oh, my Neocaridina are living happily at GH X, KH Y, TDS Z,” and that becomes your personal reference, not just a random chart.

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8. Common Beginner Mistakes With GH, KH, and TDS

A few traps that cause stress (for shrimp and humans):

1. Chasing “perfect” numbers overnight

• Suddenly adding chemicals to push pH down or up

• Doing big water changes with completely different water

• Mixing lots of things at once “to fix everything”

Shrimp hate sudden changes more than they hate less-than-perfect numbers.

2. Copy-pasting someone else’s parameters without context

• “That YouTuber keeps shrimp at GH 5, KH 0, TDS 120, so I must do that too.”

• But their water source, soil, food, and maintenance routine may be completely different.

It’s better to:

Start from your own tap water.
Adjust slowly based on your own tank’s reaction.

3. Trusting only TDS

• Seeing a “good” TDS number doesn’t always mean the water is clean.

• You still need:

  • Regular water changes

  • Siphoning debris

  • Not overfeeding

TDS is a helpful tool, not a holy number.

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9. Where This Leads: “No RO, No Distilled – Can I Still Keep Shrimp?”

Now that we know:

• Soft vs hard water (Part 1)

• What GH, KH, and TDS are (this Part 2)

The next big question is:

“If I don’t have RO or distilled water,
can I still keep shrimp safely with only my tap water?”

That will be the focus of the next article in this series.

We’ll talk about:

• Using tap water smartly

• When mixing with rainwater might help

• How soil, wood, and leaves can support shrimp

• Why choosing the right species for your water is sometimes easier than fighting your water

Because at the end of the day, this whole water journey is not about chasing perfection.

It’s about understanding what you have, then slowly building a healthy, natural ecosystem around it – at your own pace. 🌱🦐

Water Basics Series — Wander Within Life

1. Soft vs Hard Water
2. GH, KH & TDS — The Three Numbers (You’re here)
3. No RO, No Distilled: Can I Still Keep Shrimp?
4. Do We Really Need a Filter?
5. Filters for Shrimp Tanks — Flow • Intake • Media
6. How I Treat Tap Water Before It Enters My Aquarium
7. Pothos as a Natural Filter — Roots in Water, Leaves Above