Maintaining stable water chemistry is one of the most important aspects of keeping a successful reef aquarium. As corals, coralline algae, clams, and other calcifying organisms grow, they consume essential elements from the water, particularly calcium and alkalinity. Without regular replenishment, these levels can fall, leading to slowed coral growth, poor colouration, and long-term reef instability.
Seachem Reef Fusion 1 & 2 is a popular two-part supplementation system designed to make maintaining calcium and alkalinity simple, accurate, and effective. Suitable for both beginner and advanced reef keepers, Reef Fusion provides the core building blocks required for healthy skeletal growth and long-term coral success.
In this guide, we’ll explain what Reef Fusion 1 & 2 does, how to dose it correctly, target parameter ranges, and common mistakes to avoid.
What Is Seachem Reef Fusion?
Seachem Reef Fusion is a two-part reef supplement system consisting of:
- Reef Fusion 1
- Reef Fusion 2
Together, these supplements help maintain:
- Calcium
- Carbonate alkalinity
- Essential ions required for coral growth
The system is designed to provide balanced supplementation without significantly affecting ionic balance within the aquarium.
What Does Reef Fusion 1 Do?
Reef Fusion 1 is the calcium component.
It contains:
- Highly concentrated calcium salts
- Bioavailable calcium for coral uptake
Calcium is a key element used by:
- SPS corals
- LPS corals
- Soft corals (to a lesser extent)
- Coralline algae
- Clams
- Other calcifying invertebrates
Without adequate calcium, skeletal growth slows significantly.
What Does Reef Fusion 2 Do?
Reef Fusion 2 provides alkalinity support.
It contains:
- Carbonates
- Bicarbonates
These compounds help maintain stable alkalinity, which is essential for:
- Coral calcification
- pH stability
- Biological processes within the aquarium
Alkalinity is often consumed rapidly in reef aquariums, particularly those dominated by SPS corals.
Why Calcium and Alkalinity Matter
Corals build their skeletons using calcium carbonate.
To do this effectively, they require both:
- Calcium ions
- Carbonate alkalinity
If either becomes depleted, coral growth can suffer.
Low Calcium Can Cause:
- Reduced skeletal growth
- Poor coral health
- Weak coralline algae growth
Low Alkalinity Can Cause:
- pH instability
- Coral stress
- Reduced calcification rates
Maintaining both parameters together is crucial.
Ideal Reef Aquarium Parameters
Most reef aquariums perform best within the following ranges:
|
Parameter |
Recommended Range |
|---|---|
|
Calcium |
400–450 ppm |
|
Alkalinity |
7–11 dKH |
|
Magnesium |
1250–1400 ppm |
|
pH |
8.1–8.4 |
Consistency is often more important than chasing exact numbers.
Why Use a Two-Part Dosing System?
Two-part dosing systems remain one of the most popular supplementation methods because they are:
- Simple to use
- Highly accurate
- Suitable for most reef aquariums
- Easily scalable
Unlike kalkwasser or calcium reactors, two-part solutions allow independent adjustment of calcium and alkalinity consumption.
Before You Start Dosing
Before adding any supplement, test your aquarium water.
At minimum, measure:
- Calcium
- Alkalinity
- Magnesium
This establishes a baseline and helps determine actual consumption rates.
Never dose blindly.
Determining Your Aquarium’s Consumption
Every reef aquarium consumes calcium and alkalinity differently.
Factors include:
- Coral type
- Coral density
- Coralline algae growth
- Aquarium volume
Step 1
Test calcium and alkalinity.
Step 2
Wait 24 hours without dosing.
Step 3
Test again.
The difference reveals your aquarium’s daily consumption.
For example:
- Calcium drops from 430 ppm to 425 ppm
- Daily calcium consumption = 5 ppm
Similarly:
- Alkalinity drops from 8.5 dKH to 8.0 dKH
- Daily alkalinity consumption = 0.5 dKH
These values become the basis of your dosing schedule.
How to Dose Reef Fusion 1
Reef Fusion 1 increases calcium levels.
General Starting Dose
Follow the manufacturer’s instructions based on aquarium volume.
Add slowly into:
- High-flow sump areas
- Areas of strong circulation
Avoid direct contact with corals.
Important
Never mix Reef Fusion 1 and Reef Fusion 2 together before dosing.
Doing so may cause precipitation and reduce effectiveness.
How to Dose Reef Fusion 2
Reef Fusion 2 supports alkalinity.
Dose separately from Reef Fusion 1.
Many reef keepers add:
- Reef Fusion 1 in the morning
- Reef Fusion 2 later in the day
This reduces the likelihood of precipitation.
Manual Dosing vs Automatic Dosing
Manual Dosing
Suitable for:
- Small reef aquariums
- Beginner reef keepers
- Lower-demand systems
Advantages:
- Simple setup
- Low cost
Automatic Dosing Pumps
Ideal for:
- SPS reefs
- Larger aquariums
- High-demand systems
Advantages:
- Greater stability
- Reduced daily maintenance
- Consistent supplementation
Many hobbyists use dosing pumps once daily consumption exceeds a few millilitres per day.
Adjusting Doses Over Time
As corals grow, demand increases.
Re-test regularly:
New Reef Systems
Test 2–3 times per week.
Mature Mixed Reefs
Test weekly.
SPS-Dominated Reefs
Test multiple times per week.
Increase dosing gradually when required.
Avoid large adjustments.
The Importance of Magnesium
Many reef keepers focus solely on calcium and alkalinity.
However, magnesium plays a critical role.
Magnesium helps:
- Stabilise alkalinity
- Prevent calcium precipitation
- Support coral growth
Low magnesium can make calcium and alkalinity difficult to maintain.
Always monitor magnesium alongside Reef Fusion dosing.
Common Dosing Mistakes
Dosing Without Testing
This is one of the most common causes of instability.
Always verify parameters before making adjustments.
Raising Levels Too Quickly
Rapid changes can stress corals.
Aim for gradual corrections.
Ignoring Alkalinity
Many hobbyists focus on calcium while overlooking alkalinity.
In reality, alkalinity fluctuations often affect corals more noticeably.
Skipping Magnesium Testing
Imbalanced magnesium often causes recurring calcium and alkalinity issues.
Dosing Both Parts Together
Always separate dosing times.
Mixing solutions can cause precipitation and reduce effectiveness.
Signs Your Corals Need More Supplementation
Watch for:
- Slower growth
- Reduced coralline algae coverage
- Pale growth tips
- Falling test results
These signs may indicate increasing consumption.
Signs of Overdosing
Excessive supplementation can cause:
- White precipitation
- Cloudy water
- Elevated pH
- Coral stress
- Parameter instability
If levels rise too quickly, stop dosing temporarily and retest.
Example Dosing Schedule
Morning
- Dose Reef Fusion 1
Afternoon or Evening
- Dose Reef Fusion 2
Weekly
- Test calcium
- Test alkalinity
- Test magnesium
Monthly
- Review coral growth
- Adjust dosing amounts if necessary
This routine helps maintain long-term stability.
Reef Fusion for SPS, LPS, and Mixed Reefs
SPS-Dominated Reefs
High consumption.
Often require:
- Daily dosing
- Automated dosing systems
LPS Reefs
Moderate consumption.
Often suitable for manual dosing.
Mixed Reefs
Typically benefit from regular testing and gradual adjustments as coral biomass increases.
Final Thoughts
Seachem Reef Fusion 1 & 2 provides a simple, effective solution for maintaining calcium and alkalinity in marine aquariums. By understanding your aquarium’s consumption rates, testing regularly, and dosing consistently, you can provide the stable conditions corals need for long-term growth and health.
Whether you’re maintaining a beginner mixed reef or an advanced SPS system, balanced supplementation is one of the foundations of reef-keeping success. Combined with regular water testing and good overall husbandry, Reef Fusion can help keep your reef thriving for years to come.
At Charterhouse Aquatics, we stock the complete range of Seachem reef supplements, dosing pumps, water testing kits, and marine aquarium essentials to help you maintain optimal reef water chemistry.
