Chrysophytes aka “Golden Algae” in Reef Aquariums - Causes and Treatment

Reef aquariums are a beautiful representation of ocean ecosystems, but they require careful maintenance to stay balanced. Occasionally, aquarists may encounter a problem with chrysophytes, also known as golden algae or golden-brown algae. These microorganisms can cover surfaces in a reef tank, creating unsightly patches and potentially smothering corals. 

Chrysophytes have long been a challenge in reef aquariums, but their presence has become increasingly common in recent years. These organisms thrive in low-nutrient, sterile environments. While reefers previously relied on live rock to establish new tanks, the shift toward using dry rock has gained popularity because it is inherently pest-free, less expensive, and better for the environment. However, the sterile conditions created by dry rock provide an ideal habitat for ubiquitous chrysophytes to flourish.

What Are Chrysophytes?

Chrysophytes are a type of algae belonging to the class chrysophyceae. They are single-celled or colonial protists that thrive in aquatic environments. In reef aquariums, they often appear as a golden-brown film on rocks, substrate, and even corals. While not inherently harmful in small amounts, their rapid growth can smother corals and disrupt the ecosystem’s balance.

chrysophytes are known to prey on microbes, particularly bacteria, as many species within this group are mixotrophic, meaning they can obtain energy through both photosynthesis and by consuming smaller organisms like bacteria through a process called phagotrophy; essentially acting as predators on microbial prey when light conditions are not optimal for photosynthesis.

Causes of Chrysophyte Blooms

Several factors contribute to the growth of chrysophytes in reef aquariums. Understanding these causes is essential for effective prevention and treatment:

Excess Silicates: chrysophytes thrive in environments with high levels of silicates, which may come from tap water, high levels in some salt mixes, or substrate leaching.

Imbalanced Nutrients: Low levels of nitrates and phosphates, often referred to as “nutrient starvation,” can give chrysophytes a competitive advantage over other types of algae and lifeforms in the aquarium.

Low Flow Areas: Poor water circulation creates dead zones where chrysophytes can easily settle and proliferate.

Low Light Conditions: Chrysophytes can outcompete other algae in low-light environments, making dimly lit aquariums more susceptible.

New Tank Syndrome: Newly established tanks with unstable parameters are especially prone to chrysophyte blooms.

Silicate-Based Sand: Substrates made from silicate materials can leach silicates into the water, feeding chrysophytes.

How to Get Rid of Chrysophytes

Eliminating chrysophytes requires a multi-faceted approach to address their underlying causes and prevent regrowth. Here are the most effective strategies:

1. Improve Water Quality

Use RO/DI Water: Ensure that the water used for top-offs and water changes is purified using a reverse osmosis/deionization (RO/DI) system to eliminate silicates and other contaminants.

Monitor Nutrients: Test for nitrates, phosphates, and silicates. Maintain balanced levels (e.g., 5-10 ppm nitrates and 0.03-0.1 ppm phosphates) to support coral growth and outcompete chrysophytes.

2. Increase Flow

Install additional powerheads or adjust existing ones to eliminate dead spots and promote better circulation throughout the tank.

Focus on areas where chrysophytes tend to accumulate, such as the substrate and rockwork.

3. Manual Removal

If crhysophytes are encroaching on your coral, use a soft brush and a turkey baster to remove chrysophytes from rocks and other surfaces. Follow up with a water change to remove dislodged debris.

4. Reduce Silicates

Use a high-quality phosphate/silicate remover like granular ferric oxide (GFO) in your filtration system.

Check your salt mix and substrate for silicate content and switch to silicate-free alternatives if necessary.

5. Optimize Lighting

Adjust the intensity and spectrum of your aquarium lights to discourage chrysophyte growth. Aim for lighting conditions that favor coral and beneficial algae instead.

Increase the photoperiod to give competitive organisms, like coralline algae, more time to establish dominance.

6. Add Biological Controls

Introduce herbivorous livestock, Cerith snails and copepods, for example, that can help manage chrysophytes. 

7. Be Patient

If your tank is fairly immature, especially if you used dry rock, it will take time for other organisms to proliferate and outcompete the chrysophytes in good conditions.

Chrysophytes may be a nuisance, but with the right approach, you can eliminate them and restore your reef aquarium to its full glory. By addressing the root causes—such as excess silicates, poor circulation, and nutrient imbalances—you can create a stable and thriving environment for your marine life. Regular maintenance and attention to water quality will go a long way in preventing chrysophyte blooms in the future.

Photos courtesy Mina Isaac