How To Lower Calcium In Your Reef Tank

Low calcium issue REEF2REEF Saltwater and Reef Aquarium Forum


If you’re an aquarium hobbyist, you know how important it is to maintain the right balance of minerals and nutrients in your reef tank. High levels of calcium can be particularly challenging to manage, as they can lead to problems like coral bleaching and algae growth. In this article, we’ll explore some effective ways to lower calcium in your reef tank.

Understanding Calcium in Reef Tanks

Calcium is a vital mineral for coral growth and overall reef health. However, excessive levels of calcium can become toxic to corals and other aquatic life. In reef tanks, calcium levels should ideally be between 380 and 420 ppm (parts per million). Higher levels can cause issues like coral bleaching, while lower levels can hinder coral growth and health.

Testing Your Calcium Levels

The first step in managing your reef tank’s calcium levels is to test them regularly. You can use a calcium test kit to measure the ppm levels in your tank. If you find that your levels are above the recommended range, it’s time to take action to lower them.

Reducing Calcium Levels

1. Water Changes

One of the most effective ways to lower calcium levels in your reef tank is through regular water changes. This helps to dilute the excess calcium and other minerals in your tank. Aim to change around 10% of your tank’s water every week or two, depending on your tank’s size and the current calcium levels.

2. Adjusting Your Feeding Habits

Feeding your fish and corals excessively can contribute to high calcium levels in your tank. Try adjusting your feeding habits and reducing the amount of food you provide. This can help to lower calcium levels and improve overall water quality.

3. Using Calcium Reactors

If your calcium levels are consistently high, you may want to consider using a calcium reactor. These devices use carbon dioxide to dissolve calcium carbonate, effectively lowering calcium levels in your tank. However, they require careful monitoring and maintenance to ensure they’re working correctly.

4. Adding Magnesium

Adding magnesium to your reef tank can help to balance calcium levels. Magnesium helps to prevent calcium carbonate from precipitating out of the water, which can lead to high calcium levels. You can add magnesium through supplements or through regular water changes using magnesium-rich salt mixes.


Managing calcium levels in your reef tank is crucial for maintaining healthy corals and aquatic life. By testing your levels regularly and taking steps to reduce excess calcium, you can ensure that your tank remains in optimal condition. Remember to be patient and monitor your tank’s progress carefully to achieve the best results.