What is KH (Carbonate Hardness)?
KH, or Carbonate Hardness (also called Alkalinity), measures the concentration of carbonate (CO3) and bicarbonate (HCO3) ions in your water. Unlike GH which directly provides shell-building minerals, KH serves a different crucial role: it acts as your tank’s pH buffer, preventing dangerous pH swings that can kill shrimp.
Think of KH as a pH shock absorber. When acids are introduced to your tank (from fish waste, bacterial processes, or CO2), KH neutralizes them before they can dramatically change pH. Without adequate KH, these acids accumulate and cause sudden, often fatal pH drops.
Why KH Matters for Shrimp
pH Stability Is Everything
Shrimp are far more sensitive to pH changes than the actual pH number. A tank stable at 7.2 is healthier than one swinging between 6.8-7.0. KH provides this stability by:
- Neutralizing acids produced by biological filtration
- Absorbing CO2 fluctuations from plants and respiration
- Preventing pH crashes during vulnerable overnight hours
The Caridina Exception
Here’s where it gets interesting: Caridina shrimp need virtually zero KH (0-1 dKH). This seems counterintuitive - why would they want unstable pH conditions?
The answer is active substrate. Caridina tanks use buffering substrates like ADA Amazonia, Controsoil, or Brightwell that:
- Lower and maintain pH around 6.0-6.5
- Work by absorbing KH from the water
- Provide their own stable buffering system
In this setup, KH interferes with the substrate’s buffering. Adding KH forces the substrate to work overtime absorbing it, which:
- Exhausts the substrate faster
- Causes pH to rise prematurely
- Shortens the substrate’s usable lifespan
For Caridina: Use GH+ remineralizer (no KH), not GH/KH+
The KH-pH Relationship
KH and pH are intimately connected:
- Higher KH = Higher pH (carbonates are alkaline)
- Higher KH = More stable pH (better buffering)
- Lower KH = Lower pH potential (less buffering)
- Lower KH = More pH volatility (less buffering)
This is why Neocaridina keepers using tap water often have stable tanks - their moderate KH (2-8 dKH) provides natural buffering. Caridina keepers must rely on active substrate for stability since they can’t use KH buffering.
Different Species, Different Needs
Neocaridina (Cherry Shrimp, etc.)
Neocaridina thrive with moderate KH of 2-8 dKH. This provides stable pH in the 7.0-8.0 range they prefer. Most treated tap water falls in this range, making Neocaridina beginner-friendly.
Caridina (Crystal Red, Taiwan Bee, etc.)
Caridina require 0-1 dKH. Use RO water remineralized with Salty Shrimp GH+ (no KH) and active substrate. The substrate provides all necessary pH buffering.
Sulawesi Shrimp
Sulawesi need moderate KH (3-6 dKH) to buffer their high pH (7.5-8.5). Use specialized Sulawesi mineral salts that provide appropriate KH along with other minerals.
Signs of KH Problems
KH Too Low (Non-Active Substrate Tanks)
- pH crashes, especially overnight or early morning
- Shrimp deaths with no obvious cause
- pH readings varying significantly between tests
- Struggling beneficial bacteria (they need stable pH too)
KH Too High (In Caridina/Active Substrate Tanks)
- Rising pH despite active substrate
- Substrate exhausting prematurely
- pH higher than expected for substrate type
- Need to replace substrate more frequently
Active Substrate and KH
Active substrates are ion-exchange materials that trade their hydrogen ions for KH ions in your water. This exchange:
- Removes KH from the water
- Releases hydrogen ions (which lower pH)
- Creates stable low-pH conditions
- Eventually exhausts when all hydrogen ions are traded
Substrate lifespan depends on source water KH. High KH water exhausts substrate faster. This is why Caridina keepers use RO water - zero KH means maximum substrate longevity.
KH by Species Family
Different shrimp families have evolved in different environments, leading to varying kh requirements. Understanding these differences is crucial for successful shrimp keeping.
| Family | Acceptable Range | Optimal Range | Example Species | Notes |
|---|---|---|---|---|
| Neocaridina | 2-8 dKH | 3-5 dKH | Cherry Shrimp | Hardy, tolerates wider ranges |
| Caridina | 0-1 dKH | 0-0 dKH | Crystal Red Shrimp | Sensitive, requires stable parameters |
| Sulawesi | 3-6 dKH | 4-5 dKH | Cardinal Shrimp | Unique requirements, warm alkaline water |
Sensitive, requires stable parameters
Unique requirements, warm alkaline water
Stability Over Perfection
While hitting optimal ranges is ideal, stability is more important than exact numbers. Consistent parameters within the acceptable range are better than fluctuating values that occasionally hit optimal.
How to Test KH
Accurate testing is essential for maintaining proper kh levels. Here are the most common testing methods, each with their own trade-offs.
Liquid Test Kit (Drop Count)
Pros
- Accurate dKH measurement
- Easy to interpret color change
- Long shelf life
Cons
- Takes a few minutes
- Requires careful drop counting
Test Strips
Pros
- Quick and convenient
- Multi-parameter strips available
Cons
- Less accurate
- Hard to read low KH values
- Can't detect 0-1 dKH accurately
Quick Comparison
| Method | Accuracy | Cost | Best For |
|---|---|---|---|
| Liquid Test Kit (Drop Count) | High | $$ | Recommended choice |
| Test Strips | Low | $ | Quick checks |
Testing Tip
Test at the same time of day for consistent results. Water parameters can fluctuate based on feeding, lighting, and CO2 levels. Morning tests before lights-on often provide the most stable readings.
How to Adjust KH
Sometimes you need to adjust your kh levels. Here are safe methods for both raising and lowering values. Always make changes gradually - sudden parameter swings can stress or kill shrimp.
How to Raise KH
Increase kh levels
Remineralizer with KH (GH/KH+)
Use Salty Shrimp GH/KH+ instead of pure GH+ to add carbonate buffer
Crushed Coral
Add to filter or substrate for gradual KH increase
Aragonite Substrate
Calcium carbonate substrate that buffers and raises KH
Warnings
- DO NOT raise KH in Caridina tanks with active substrate
- Raising KH also raises pH - monitor both
- Avoid baking soda - unstable and can cause pH swings
How to Lower KH
Decrease kh levels
RO/DI Water Dilution
Replace tank water with pure RO water to dilute carbonates
Active Substrate Absorption
Active substrates like ADA Amazonia absorb KH naturally
Peat Moss
Filter through peat moss to reduce KH
Warnings
- Lower KH means less pH stability - monitor for pH swings
- Active substrate has limited KH absorption capacity
- Very low KH can lead to pH crashes
Critical Safety Notice
Never make sudden, large changes to water parameters. Shrimp are extremely sensitive to parameter swings. All adjustments should be made gradually over hours or days, not minutes. When in doubt, go slower. Test frequently during adjustments to monitor progress.
KH FAQ
GH measures calcium and magnesium (hardness minerals for shells), while KH measures carbonates and bicarbonates (buffer capacity for pH stability). They're often confused but serve completely different purposes. You can have high GH with low KH or vice versa depending on your water source and additives.
Caridina tanks use active substrates that lower and buffer pH around 6.0-6.5. These substrates work by absorbing KH from the water - the KH absorption is what maintains the low pH. If you add KH, the substrate exhausts its buffering capacity faster, pH rises, and the substrate 'expires' sooner. Zero KH lets the active substrate do its job properly.
A pH crash occurs when pH drops suddenly and dramatically, often overnight. In tanks with very low KH (0-1), there's no buffer to resist pH changes from normal biological processes like CO2 production and nitrification (which produces acid). KH acts as a buffer - it absorbs these pH-changing substances and keeps pH stable.
Active substrates typically last 12-24 months before their buffering capacity is exhausted. Lifespan depends on your source water KH - higher KH means faster substrate exhaustion. Signs of exhausted substrate include rising pH and KH readings. Some keepers replace the top layer annually rather than the entire substrate.
While baking soda (sodium bicarbonate) does raise KH, it's not recommended for shrimp tanks. It creates unstable buffering that can lead to pH swings, and it adds sodium to your water. Purpose-made aquarium buffers or GH/KH+ remineralizers provide more stable, shrimp-safe results.
KH naturally decreases due to biological processes. Nitrifying bacteria consume carbonates, and the nitrogen cycle produces acids that get neutralized by KH. In planted tanks, CO2 consumption during photosynthesis can also affect KH. Regular water changes with properly mineralized water maintain stable KH.
Track Your KH with ShrimpKeeper
Stop guessing. Start tracking. ShrimpKeeper gives you species-specific kh ranges, instant diagnostics, and historical graphs for your colony.
KH Problems & Troubleshooting
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