Yellow Tangs (zebrasoma flavescens) can help control nuisance algae in saltwater aquariums 100 gallons or larger.

The most common problem marine aquarists battle is with nuisance "algae." I put the word algae in quotes because not everything we aquarists refer to is actually a true algae. Much like reef keepers often describe the animals they keep collectively as “corals” when they are really referring to an assemble of corals with anemones, clams, corallimorphs, and colonial polyps, but I digress.

We have true algae such as Bryopsis and Derbisia, the dual plague hair algaes. There are also diatoms, the bane of new aquariums. Then there are dinoflagellates, the so-called snot algae. And finally, there are various cyanobacteria, which are actually photosynthetic bacteria, not an alga at all, that look like a small child decided to cover the display’s sand and rockwork with fruit rollups.

Even though these are all very different life forms, the root causes and cures are fortunately similar. Generally speaking, nuisance “algae” can be dealt with successfully by nutrient control:

Using a clean source of water is extremely important. There is no sense is worrying about nutrients in the aquarium if every time the aquarist does a water change or tops off the aquarium for evaporation, they are dosing the system with nutrients from the tap. Tap water can have up to 10 ppm nitrate in it and my local water supply authority adds up to 1 ppm zinc orthophosphate as a rust inhibit for the pipes. This much phosphate (not to mention the zinc) can wreak havoc on a closed aquatic system.

Sailfin Tangs (zebrasoma desjardinii) are a great choice for 140 gallon or larger reef aquariums and are known for having a voracious appetite for algae.

For most people, I would recommend a reverse osmosis unit (RO for short) or a combination reverse osmosis and deionization unit (RO/DI). These are fairly easy to operate and can produce high-quality clean water. The only downside to these units is they waste 3-5 gallons of water for every gallon of good product water they produce. They also tend to produce a slow flow of water. They are generally rated in how many gallons of water they can produce in a day, and they mean a full, 24-hour day. This rating is also under ideal circumstances of temperature and water pressure so as the pressure drops or the temperature declines seasonally, the production of the reverse osmosis unit drops off.

Reverse osmosis membranes tend to remove 90-98% of the contaminants in tapwater. Because of this, many manufacturers add a deionization stage post reverse osmosis membrane to remove the remainder of the contaminants. This makes an even higher grade of water, but adds another component that requires maintenance and periodic replacements.

Deionization-only units come in two styles. The most common one is a mixed bed, where the anion and kation resins are combined in one vessel. These are relatively cheap, but require frequent replacement. Separate resin bed units are uncommon, but are generally far larger than mixed bed units, so they last longer/can produce more water than a smaller unit before requiring maintenance and these separate resin systems can be recharged with household chemicals. While these chemicals can usually be found at various hardware stores, they can also be dangerous when mishandled, so evaluate this when deciding if a separate resin unit is appropriate.

A high-quality salt mix is also critical for success in marine aquarium keeping. Think about it: the saltwater itself is the very basis of any marine aquarium. It only stands to reason to use a high-grade mix. A good salt should be phosphate and nitrate-free. It makes no sense to utilize a mix full of nutrients only to later spend good money to strip the saltwater in the tank of those same nutrients.

Also note that most brands of salt are made to be tapwater safe. Since tapwater has a certain amount of calcium and alkalinity, those same brands would require supplementation to reach optimum levels when mixed with a purified source of water that has been stripped of the tapwater’s original calcium and alkalinity.

This hair algae infestation was caused in part by overfeeding. Notice the excess uneaten pellet food in the sandbed.

Overfeeding is one of the most common faults of newer aquarists. Excess, rotting food quickly dissolves to become excessive nutrients in the water, which in turn fuel various nuisance algae. This does not mean I don’t want people to feed their aquariums. I just want them to be sure that the food they are providing is being used by something. The fish should eat anything provided in a matter of minutes. Watch that a lot of the food is not captured by filters or washed over into overflow boxes. Are the corals getting some of the food as it drifts down from the surface or is it being blown behind the rockwork in the display instead? Target feeding the corals, while certainly more tedious, does ensure that the food is not being wasted and is going to the proper corals. In a nutshell, whatever food is added to the aquarium has to be eaten and used by the animals or removed via export methods I will discuss next. If it is neither eaten nor removed, something else will use that energy, usually nuisance algae.

Refugiums are becoming increasingly popular in marine aquarium keeping. While there are many, many different styles of refugiums, I want to focus on those designed for nutrient export and growing algae. The easiest way to think about this is the more algae grown in a refugium, the fewer nutrients available in the water column and therefore the less algae that grows elsewhere like in the display.

There are a number of different algae that have been used for nutrient export in refugiums: Chaetomorpha, Caulerpa, Ulva, Gracilaria, Sargassum, turf algae, etc. Chaetomorpha is probably the most popular because it is easy to grow, tolerates a wide variety of lighting conditions, is relatively non-invasive, is stable in that it is not prone to a sexual phase when the parent crashes, and easy to prune and harvest. Plus, it is not illegal anywhere like the previously popular Caulerpa which has been mostly banned for sale in California due to concerns about it being released into the local environments and spreading unchecked.

Protein skimming or foam fractionation is yet another method of nutrient export. They are exceptionally good at removing many organic compounds before they have a chance to decompose and breakdown releasing even more nutrients into the water. And simply put, once an aquarist has seen and more importantly smelled the mud produced by an effective protein skimmer, they will never want their aquariums to be without one. There is an ever-increasing multitude of protein skimmer manufacturers, models, and designs out there. It seems everyday a new one comes to market. Just be sure to get one that can routinely produce a lot of small bubbles and that it is appropriately sized for the system.

Overfeeding is one of the most common faults of newer aquarists. Excess, rotting food quickly dissolves to become excessive nutrients in the water, which in turn fuel various nuisance algae.

Activated carbon has been used in aquarium keeping for decades. It removes organic compounds much like protein skimming does but whereas the protein skimmer removes the organics completely from the water column by lifting and removing them to the collection cup, activated carbon remains in the water until it is physically removed by the aquarist doing routine maintenance. I believe activated carbon is useful and does have its place in a marine system’s design and overall husbandry. I don’t believe though that it is a replacement for protein skimming, just a nice complement. Also, be sure to locate the carbon in a place where it is convenient to access for regular replacement.

A new type of chemical filtration media has become popular as of late, the use of granular ferric oxide as a phosphate remover. This type of media is better at targeting phosphate removal, although they do remove some silicate and organics as well. I prefer to use this media in a reactor vessel. These gently tumble the media so that every piece is exposed to the aquarium’s water to maximize removal. I have been very successful in using two reactors in series, with the first one filled with activated carbon and the second unit filled with granular ferric oxide. In this setup, water flows through the activated carbon first and from there into the second reactor with the phosphate remover. This way there is only one pump necessary to operate both reactors and both media get good exposure to the aquarium water.

The last component of a properly designed marine system to minimize nuisance growths of algae is an appropriate compliment of grazers. Algae eating fish, mollusks, echinoderms, and crustaceans are an important part of reducing algae growth. Maintaining a mix of these creatures is essential to keeping algae in check as these all tend to favor a different type of algae as their preferred food. Ever drive past a field of cows to see the grass grazed low, but big tall stands of some sort of weed? That is because the cows don’t like to eat that particular weed. The same sort of thing will happen in an aquarium. If there is only one type of grazer, it is likely that one particular type of algae that those grazers don’t eat will flourish unchecked.

Hopefully, armed with this knowledge, you will be able to fight the good fight against nuisance algae and work towards maintaining a beautiful display aquarium. If things start to go awry, be sure to reevaluate the husbandry and stocking of the system to attempt to correct the underlying issue instead of simply masking the problem with quick fix solutions.