Alkalinity And Calcium Dosing Methods

Maintaining proper calcium and alkalinity levels is one of the most critical aspects of reef aquarium water chemistry. After years of reef keeping and testing virtually every dosing method available, I can safely say that understanding aquarium dosing systems is not just important, but it is fundamental to long-term success as a hobbyist. 

If your alkalinity levels keep dropping or you are new to aquarium dosing, in this article, we will go through the different dosing methods to keep alkalinity and calcium levels stable. 

Why Is Calcium & Alkalinity Important In Reef Aquariums?

A successful reef aquarium has a delicate balance of calcium ions and carbonate alkalinity to support corals and coraline algae. As corals grow, they use the calcium and carbonate ions to form calcium carbonate, which they use to build their exoskeletons. This process happens 24/7 in a thriving reef aquarium system. 

What many reef hobbyists don’t realize is that a standard 100-gallon reef tank with moderate coral growth consumes around 20 ppm of calcium and 2.8 dKH of alkalinity every day. While that may not sound like a lot, over a month, that is 600 ppm of calcium and 84 dKH of alkalinity that needs replacing.

Without properly supplementing your reef aquarium, your system’s calcium and alkalinity levels will crash within weeks, leading to poor coral growth, tissue recession, and eventually coral death. 

Two-Part Dosing Systems

Two-part dosing systems have dominated the reef hobby for a very good reason. These dosing systems are pretty much foolproof, plus they can be scaled for nano aquariums to larger reef aquariums. 

Two-Part Dosing Systems: The Alkalinity Component

• Sodium bicarbonate starts by lowering the pH, then stabilizes

• Sodium carbonate increases the pH

• Sodium hydroxide significantly increases pH

Most aquaiums benefit from carbonate or hydroxide-based systems due to the CO2 buildup from poor ventilation, unless your aquarium system is already running a high pH level above 8.4. 

Two-Part Dosing Systems: The Calcium Component

Calcium chloride is the typical choice as it has a high solubility. Moderate daily dosing can increase salinity by 7.5 ppt annually. This does require ongoing salinity management through freshwater additions or switching to a three-part system. This adds maintenance costs that newbie reefers may not be aware of. 

Kalkwasser

Kalkwasser (limewater) is one of the most popular alkalinity and calcium dosing methods in the hobby. It works by dissolving calcium hydroxide in freshwater to create a solution containing calcium and hydroxide ions. The hydroxide provides alkalinity after reacting with CO2 - atmospheric and tank CO2 is converted into bicarbonate and carbonate, which corals use for calcification. 

Kalkawasser dosing does, however, have some limitations:

• The solubility limit restricts you to around 2 tsp per gallon of freshwater.

• For tanks with demanding alkalinity and calcium levels, kalkwasser dosing may provide insufficient supplementation even if you replace all evaporated water.

• The high pH level of kalkwasser requires very slow and careful dosing.

• Kalkwasser is highly caustic, so extra care is needed when using it.

Calcium Reactors

If you have a high-demand system, calcium reactors offer industrial-strength solutions. These calcium carbonate systems provide amazing capacity and long-term stability for reef tanks. They work by reducing pH to approximately 6.5 inside a reaction chamber, dissolving aragonite media, which release calcium and bicarbonate ions. 

What we love about calcium reactors is their scalability. While kalkwasser dosing can replace approximately 4% of tank volume per day, calcium reactors can support tanks consuming 10 dKH or more of alkalinity per day. For SPS coral enthusiasts, calcium reactors are preferred because of the constant dosing and high-level supplementation they provide. 

However, this amazing capacity comes with trade-offs. Calcium reactors maintain pH around 6.5, and even with a secondary chamber to improve CO2 utilization, most reef tanks run 0.2 to 0.4 pH units below optimal levels. Many calcium reactor users compensate for this by also using the kalkwasser method to support pH levels. 

Calcium reactors have a reasonable upfront cost, but you also need to consider the costs of CO2 equipment and media. You also have ongoing costs such as CO2 refills and media replacement, plus good quality aragonite media has a significant upfront investment. These systems also require space for reaction chambers, CO2 cylinders, and dedicated plumbing and equipment areas, which make calcium reactors less suitable for living room or school reef tank displays. 

One-Part Dosing Systems

Products that use calcium acetate dose calcium directly while allowing bacteria to metabolize the acetate into bicarbonate activity. The acetate also serves as a carbon source for denitrifying bacteria, which can reduce nitrate levels. 

While calcium acetate reduces equipment costs and dosing complexity, the price is quite high. For nano-reef tanks with low consumption, this premium price may be justified by how convenient it is. For larger aquarium systems, the yearly running costs become prohibitive quickly. 

Which Dosing System Is Best For Your Aquarium?

Small Reef Tanks (<0.5 dKH daily)

For reef tanks with fish-only and only small amounts of coralline algae, or a softie-only coral tank that consumes less than 0.5 dKH alkalinity per day, we recommend the following:

• Two-part dosing

• Kalkwasser as top-off water

• Calcium acetate

Mixed Reef Tanks (0.5 - 2 dKH daily)

For reef tanks with moderate SPS corals, we recommend the following:

• A quality two-part system with proper ion balancing 

• Kalkwasser with two-part backup

• A small calcium reactor

SPS-Dominated Tanks (>2 dKH daily)

For high-demand reef tanks with fast growth rates, we recommend the following:

• Reactor plus kalkwasser to support with maximum capacity

• Calcium reactor as a primary dosing method

• Large two-part dosing for sustained high consumption

Dosing Aquariums - Reefco Aquariums Top Tips!

• Before dosing, adjust the alkalinity and calcium levels - starting with balanced conditions makes it easier to control. We recommend getting a high-quality dosing controller system. 

• Test alkalinity because it responds much faster to dosing changes, and use it as your primary monitoring parameter.

• Test the conditions every week. For heavily stocked reef tanks, you should test this twice a week. 

• Select a dosing rate based on consumption testing. If consumption patterns change drastically, adjust the dosing slightly until it stabilizes. 

• As corals grow, the consumption rate will increase. As your reef tank matures, allow 20 to 50% increases in dosing.

Summary

The perfect aquarium dosing doesn’t exist. Dosing your aquarium should match your system's specific needs and maintenance requirements. You corals don’t care what fancy brand you choose, but that you are familiar with balancing calcium and alkalinity in the water. 

You should select an alkalinity and calcium dosing method that you can implement reliably and afford - that is the key to long-term success! If you would like to learn more about dosing methods or what we use in-store, contact the Reefco Aquariums team today for help. Happy reefing!