Calcium Levels Are Stable, But The Alkalinity Level Keeps Dropping: What Can I Do?
Have you tested your water parameters and noticed something puzzling - your calcium levels remain stable, but your alkalinity level keeps dropping despite providing the best care possible. If this sounds familiar, do not worry, you are not alone. This imbalance has frustrated many aquarium hobbyists, from beginner reefers to experts with years of reefing experience.
Let’s take a close look at why this can happen and what solutions you can try to restore the balance in your reef aquarium.
The Relationship Between Calcium And Alkalinity In Aquariums
Calcium and alkalinity have a delicate relationship in aquatic ecosystems. While the two parameters are often discussed together, they can behave independently in aquariums, creating confusing situations similar to the one you are currently experiencing.
Calcifying reef organisms such as SPS and LPS (stony) corals, clams, mollusks, and coralline algae consume calcium and alkalinity in fairly fixed proportions. For example, when conditions are stable, for every 1dKH of alkalinity they use, they consume around 6 to 7 ppm of calcium. This balanced consumption of calcium and alkalinity means that they drop together.
So, if this is the case, you may be thinking "Why is the calcium stable while the alkalinity is decreasing”?
Why Can Alkalinity Drop While Calcium Remains Stable In Reef Aquariums?
-
Coral Growth
One of the most common reasons for alkalinity dropping is that your corals are thriving! Fast-growing SPS corals and coralline algae are known for consuming alkalinity during periods of rapid growth. As SPS corals grow, they consume alkalinity to build their skeletons, in a process called calcification. During this process, these coals and algae may consume alkalinity faster than your current alkalinity dosing schedule.
-
Inconsistent Testing
Sometimes the problem isn’t inside your aquarium, but your testing method(s). Basic water test kits are a good start, but they are not as reliable and precise as lab-grade testing kits.
-
Carbon Dioxide (CO2)
Carbon dioxide (CO2) plays a key role in aquarium water chemistry. In the surrounding air, CO2 dissolves in the aquarium water and reacts with calcium carbonate to form bicarbonate, which can affect alkalinity levels. If your reef tank is experiencing poor gaseous exchange, it may be contributing to alkalinity dropping without affecting calcium levels.
-
Aquarium Salt Mix
Reef salt is important to maintain a stable ecosystem in saltwater aquariums. Some salt mixes may not contain enough alkalinity-supporting minerals, which may be causing the alkalinity to drop while calcium remains stable. Improper mixing of aquarium salt or using a poorly-mixed salt can also lead to alkalinity dropping in a reef tank.
Solutions To Stabilizing Alkalinity Levels In Reef Aquariums
Now that we have identified the possible causes of alkalinity dropping in reef aquariums, let’s look at the different solutions to maintaining balanced alkalinity levels inside aquariums.
Two-Part Dosing
If you use a two-part dosing solution (separate alkalinity and calcium supplements), you may want to increase alkalinity independently. We recommend starting by increasing the alkalinity by 10% while maintaining your current calcium dosing schedule. Monitor both alkalinity and calcium closely for one week, testing the water every day to see how your system is responding before making any adjustments.
NOTE: Always make small, incremental changes to maintain tank stability.
Using A Calcium Reactor
For hobbyists using calcium reactors, you have two options:
-
Increase CO2 input: This increases both calcium and alkalinity. It is important to monitor pH carefully, as excessive CO2 levels can lower water pH.
-
Increase effluent flow rate: Faster flow increases media dissolution, which provides more calcium and alkalinity to your aquarium system.
Calcium Hydroxide Dosing
Kalkwasser (calcium hydroxide) dosing offers unique benefits - not only does it increase alkalinity and calcium, but it also consumes CO2 to form carbonate alkalinity, which increases the pH level.
The key to kalkwasser dosing is patience - you must dose it slowly and constantly. We suggest 150 equal increments throughout the day (approximately one dose every 9 minutes). This should prevent any rapid pH spikes which can trigger calcium carbonate precipitation, which would remove alkalinity and calcium from the water.
Aquarium Dosing Tips
Whether you use an automated or manual dosing method, we have some top tips to help optimize alkalinity levels.
Automated Dosing Systems
-
Consistency is key. Many hobbists have found that a litermeter with 150 equal increments throughout the day works well.
-
If possible, keep alkalinity supplements in separate reservoirs from calcium supplements.
-
Ensure that your dosing pump is delivering the correct amount, calibrating the system frequently.
Manual Dosing
-
Divide your daily dosing into two separate schedules - we recommend morning and evening.
-
Always mix powdered supplements with distilled water before supplementing your aquarium.
-
When adding supplements, dose away from powerheads and return pumps.
Monitoring Alkalinity & Calcium In Aquariums
Effective alkalinity and calcium management require consistent testing. You should:
-
Test the parameters at the same time every day, as alkalinity naturally changes throughout the day because of CO2 exchange and coral activity
-
Track everything - this includes changes in dosing, coral growth, equipment settings, and parameter readings.
-
Look for patterns - is the alkalinity level dropping faster when there is more light, after you feed livestock, etc.
-
Quality control your testing kits for accuracy.
Aquarium System Changes To Improve Alkalinity & Calcium
If you have done everything to optimize your aquarium dosing, but you are still having issues with alkalinity stability, you may want to try the following:
-
Upgrade to a calcium reactor if you have a heavily stocked aquarium
-
Evaluate your aquarium’s biological load
-
Assess your aquarium equipment - check that your protein skimmer, gas exchange systems, and circulation pumps are functioning properly.
Conclusion
Maintaining stable calcium and alkalinity levels is key to a thriving reef tank. Understanding the chemistry and implementing correct dosing strategies will help restore balance in your reef tank and ensure your corals are thriving.
If you would like to learn more about calcium and alkalinity in reef tanks or what dosing methods will be best for your aquarium setup, contact the Reefco Aquariums team!
