Complete Guide to Coral Tank Water Quality Parameters: Adjusting KH, Mg, and Ca | ブリちょく
Coral| ✍️ BreederDirect Editorial
Complete Guide to Coral Tank Water Quality Parameters: Adjusting KH, Mg, and Ca
A detailed guide to essential water quality parameters for coral keeping (KH, Mg, Ca, NO3, PO4), including ideal ranges, measurement methods, and adjustment procedures. Also covers types of supplements and how to use them.
Key Takeaways
A detailed guide to essential water quality parameters for coral keeping (KH, Mg, Ca, NO3, PO4), including ideal ranges, measurement methods, and adjustment procedures. Also covers types of supplements and how to use them.
Managing water quality parameters is essential for keeping corals healthy. "I do water changes now and then, but my corals aren't doing well" or "What supplements should I buy?" If you've had these questions, this guide explains the role and adjustment methods for each of KH, Mg, Ca, NO3, and PO4 in easy-to-understand terms.
✍️
BreederDirect Editorial
The BreederDirect editorial team specializes in care information for animals, covering veterinary care and breeding to deliver beginner-friendly guides.
Find Coral on BreederDirect
Buy directly from verified breeders
Browse Related Listings
Find Coral listings related to this article on BreederDirect. Buy directly from verified breeders.
Five Essential Water Quality Parameters for Corals
Coral skeletons are composed of aragonite (calcium carbonate). To build their skeletons, corals consume large amounts of calcium (Ca) and bicarbonate ions (KH). Meanwhile, magnesium (Mg) is an unsung hero that stabilizes the balance between Ca and KH.
On the other hand, nitrate (NO3) and phosphate (PO4), collectively called nutrients, cause coral bleaching and growth inhibition at high concentrations.
Simply monitoring these five parameters will greatly increase your success rate in coral keeping.
Role: Like NO3, moderate amounts are necessary, but excess causes browning
If PO4 approaches 0, bleaching can paradoxically occur. Rather than aiming for zero, "stable and low" is ideal.
Measurement Methods: Choosing Reliable Test Kits
The first step in water quality management is accurate measurement. Inexpensive test kits have high variance and lead to incorrect conclusions.
Recommended Measurement Methods
Parameter
Recommended Products
KH
Hanna Instruments HI772, Red Sea KH Test Kit
Ca
Red Sea Ca Pro, Salifert Ca
Mg
Salifert Mg, Red Sea Mg Pro
NO3
Hanna HI97781, Salifert NO3
PO4
Hanna HI736 (ULR), Red Sea PO4 Pro
For PO4 in particular, since measurement at low concentrations is necessary, Hanna photometers with ULR (Ultra-Low Range) capability offer the highest reliability.
Measurement Frequency Guidelines
- Initial setup and troubleshooting: 3+ times per week
- Stable tanks: 1–2 times per week (KH can be daily)
- Stable, established aquariums: Once per week
Measuring at the same time and under the same conditions each time makes comparisons easier.
Adjustment Procedure: Adding Supplements in the Correct Order
When correcting parameters, order matters. Skipping steps or doing them out of order can backfire.
Step 1: Adjust Mg First
If Mg is low, added Ca and KH will precipitate and be ineffective. First, adjust Mg to approximately 1,280 mg/L.
Example adjustment: If Mg is 1,150 mg/L
Add small amounts of magnesium chloride or magnesium hydroxide-based supplements, working toward the target value over several days. Avoid raising it by more than 50 mg/L per day.
Step 2: Adjust KH
Once Mg is stable, bring KH to your target. If KH is low, use sodium bicarbonate (baking soda) or commercial alkalinity supplements.
Tip: Don't raise KH by more than 1 dKH in a single dose. Too-rapid changes cause coral bleaching.
Step 3: Adjust Ca
Once KH reaches your target, adjust Ca. Calcium chloride-based supplements are standard.
---
Adjusting nutrients (NO3 and PO4) requires a different approach. If they are high, implement the following:
Review feeding amount and increase water changes
Enhance protein skimmer performance
Use activated carbon or absorbent media (Rowaphos, Purigen, etc.)
Denitrification (carbon-source dosing for NO3 cases)
If too low, increase feeding slightly or supplement with dedicated nutrient additives (like Red Sea NO3:PO4-X).
Types of Supplements and How to Choose
Supplements fall into three main approaches. Choose based on your tank size and coral type/quantity.
Manual Dosing
The simplest method and best for beginners. Add fixed amounts daily in small increments. Red Sea's "Reef Foundation" series (2-part or 3-part products) is easy to use.
Best for: 60–90 cm tanks, soft coral to LPS dominated systems
Kalkwasser (Calcium Hydroxide)
A classic method that supplements Ca and KH while replacing evaporated water. Cost-effective and simple to manage.
Best for: Tanks with high evaporation and small amounts of SPS mixed in
Two-Part Dosing
Separate Ca and KH supplement solutions dosed daily via automated dosing pumps. Red Sea's "AB+" and AquaForest's "Component 1+2+3" are well-known examples.
Best for: 90+ cm SPS-dominated tanks with high coral loads and consumption rates
Calcium Reactor
An automatic device using CO2 and coral sand (aragonite) to continuously supply Ca and KH. Low operating costs and ideal for large tanks, but requires initial investment and adjustment.
Best for: 120+ cm SPS-heavy reef tanks
Summary: Take Your Time, Adjust Gradually
The most important aspect of water parameter management is avoiding sudden changes. By repeating the cycle of measurement, recording, gradual adjustment, and re-measurement, your tank will stabilize over time.
It may seem difficult at first, but once you establish a routine, it's just 15 minutes of work per week. Start with just KH, Ca, and Mg, and once they're stable, progress to managing NO3 and PO4.
Rather than fixating on individual numbers, develop the ability to view your tank through long-term trends. This perspective is what makes coral keeping so rewarding.
