Why Coralline Algae Turns White

Branches of coralline algae

Ed Reschke/Getty Images

Coralline algae, the crusty red coating on most live rock and at the edges of your saltwater aquarium, is a common component of a healthy reef. Sometimes, your coralline algae may start to turn white and lose its pink hue. Why does this happen and how can you protect your coralline algae from turning white?

Coraline Algae

Coralline algae is a group of red algae (Rhodophyta) that contain calcium carbonate in their cell walls. This gives them their crusty texture and are frequently red or pink in coloration. They are a common algae found in coral reefs, contributing to the aquatic ecosystem.

Where Coralline Algae Is Found

There may be as many as 10,000 species of red algae found in oceans all around the world. Coralline algae usually enters your tank on live rock or coral plugs. Once established, it can climb all over your aquarium, often on the live rock and other hard, immobile surfaces in addition to the sides of your tank and equipment. If left to its own devices, it can gunk up various mechanical components, including powerheads and mechanical filtration.

What Causes Coralline Algae to Turn White

Due to its calcium carbonate structure, when the algae dies, it leaves behind its white exoskeleton. This is very similar to hard corals that lose their zooxanthellae during the bleaching process. Although these species are found in different groups and have distinctive structures, when their internal algal cells depart, they leave behind the crunchy, white outer coating.

There are many environmental conditions that can cause coralline algae to abandon their homes. Again, these causes can be very similar to influences that will cause your hard corals to also bleach. Among the most common causes are shifts in pH, temperature, and light.

pH Level in Your Saltwater Aquarium

The pH of your saltwater tank needs to be much more precise than your freshwater tank. Most marine species—fish and invertebrates included—have a very narrow optimum pH range. If the pH strays too far acidic or alkaline, you could lose all your aquarium inhabitants. In order to keep your pH stable, you will need to monitor your tank's kH (carbonate hardness), or alkalinity. The alkalinity buffers the pH, preventing rapid shifts, and is made up of the carbonates in the water. These are the same carbonates that your coralline algae will use to build their homes. Your tank's alkalinity is not an infinite supply, but it can be regularly augmented through water changes or the breakdown of other carbonate containing tank materials, such as sea shells.

When mixing the salt water for your aquarium, it is critical that you choose the correct salt mix, depending on if you have corals or just fish. These mixes will be vastly different in the buffering components they contain.

Temperature of Your Saltwater Aquarium

Another critical parameter for saltwater aquariums is temperature. In order to maintain the correct environmental temperature, you will need reliable heaters and good water movement. Don't forget that even if your heater is properly working, you still need consistent water flow around your tank to avoid any cold spots. Coralline algae stuck in a cold spot will often turn white due to poor environmental conditions.

Don't rely on your aquarium thermometer on its own, especially in nano systems. In addition to a backup heater, be sure to have a reliable digital thermometer to double check that your heater is working properly. In nano tanks, small heaters are notorious for not holding a consistent temperature and bouncing around an "acceptable" range. If your heater is unable to maintain consistent temperature throughout the day, you may need to add other insulating components or put your tank in another area.

Light in Your Saltwater Aquarium

Light is thought to be the most critical component when it comes to making your algae and corals healthy. Not all algae and corals will like the same type of light spectrum, intensity, and length of time. The photoperiod of your tank, or the amount of light your tank is exposed to, is sometimes a difficult element to manipulate. Depending on where your tank's species are found in the world, they may have varying requirements for light, which can also change seasonally. If you are having bleaching problems, research the correct lighting for your species and adjust your lights to provide the correct timing and intensity.

How You Can Fix Coralline Algae That Turns White

Once your coralline algae turns white, there is no getting it back. But once you notice a part has started to turn white, it is time to start looking at your water quality parameters. If your pH and temperature are consistent throughout the day, it's time to start backing off your lights. It may take multiple rounds of experimentation to make your coralline algae healthy. Keep in mind that by messing around with some light settings, you may upset corals in your tank. It can be a difficult balance to keep everything happy at once if they come from various parts of the world.

How You Can Prevent Coralline Algae From Turning White

It can be difficult to prevent coralline algae from turning white, but you can try to stop it before it takes over your entire tank population. The best preventive measure is regular water quality testing using a liquid-based test kit opened within the last year. Be sure to read all testing instructions thoroughly and write down your results in order to catch any trends. Test at various times throughout the day since your pH and temperature will change based on the photoperiod you have selected for your aquarium.

Article Sources
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  1. Vásquez-Elizondo RM, Enríquez S. Coralline algal physiology is more adversely affected by elevated temperature than reduced pH. Sci Rep. vol. 6, 2016