After being in the hobby for almost 23 years and having kept reef aquaria for most of them, it is still amazing that the most frequently asked question is still how to eliminate problem algae. After trying just about every method for doing this out there really are two simple answers: reduce your bioload and feeding or give up on eliminating algae and learn to control it. While there are still some hobbyists out there that feel that having algae within the confines of their display tank is a good idea, this is now more of the exception than the rule. Not only is algae unsightly, but it also increases the amount of time that needs to be spent in managing the tank and if left unchecked it can reduce the health of the animals present. In the best-case scenario, it will leach yellowing compounds into the display tank; in the worst case it will overgrow and suffocate the corals or damage corals by having the holdfasts burrow through soft tissue or smother the polyps on stony corals. Regardless of which technology or methodology is used, this problem is still the most frequently encountered in the hobby. It does not matter if algae only cover the live rock or produce a quick film on the front glass it is still a problem. For a reef tank or any saltwater tank to be successful the quantity of algae must be kept to a bare minimum otherwise the tank’s other inhabitant’s will suffer. This does not apply only to microalgae, but also about the so-called desirable types of algae such as Caulerpa and Halimeda. The only algae that is considered desirable is coralline, and that is primarily because it prevents or retards the growth of these other less desirable types. Many of the unwanted types of algae that enter our tanks do so as unwanted stowaways on the live rock and corals that we add to our tanks or even as spores in the air. It is impossible to prevent algae from being introduced into our tanks, but it is possible to keep the algae from overgrowing our tanks.
To understand how to get rid of unwanted algae it is necessary to first understand exactly what algae are? Algae are the simplest forms of plant life on the planet and have been around in one form or another for over 200 million years. Micro algae are the single celled type that can only be determined by a microscope and a good reference guide. Macro algae are the larger types of algae that to the casual observer resemble terrestrial plants. Actually these plants are really only slightly more advanced than the micro algaes in that they have defined structures such as stolons for attachment and petioles that resemble leaves. Since these plants are so primitive it makes it difficult to completely eradicate them, even when none are seen there is still enough material present so that when conditions are right the algae will grow again rapidly.
For those of you keeping Caulerpa you may be asking yourself why should I get rid of my Caulerpa since it looks so nice in my aquarium. First it is not natural for macro algaes to be growing around corals, as for the most part algaes are restricted to the turf zone or lagoon in most instances and are not part of the reef itself. This is because in these areas the grazers usually keep their growth in check. In addition, the corals are actually harmed by algae in that the algae will eventually overgrow the coral and the algae’s holdfasts can bore into soft corals. The algae may also produce compounds or antibiotic like substances that inhibit coral growth. Also for those of you that have viewed some of the public aquaria housing algae you will have noticed that the water is yellow. This is also a result of substances produced by the algae and this reduces the amount of light that can penetrate the water that further inhibits the coral’s ability to thrive. It is my opinion that a reef tank will be much more successful long term when most algae are kept to a minimum or when they are kept out of the main display tank and housed in a refugium. More hobbyists have probably left reef keeping due to algae problems than for any other reason.
Now hopefully you are dissuaded from trying to keep algae in your aquarium you are now wondering how to get rid of it. The best way to get rid of algae is to limit it from the start. That is, from when you first get your live rock you should start trying to limit the conditions that enhance algae growth. If your tank is already set up this situation will be discussed below. Getting rid of and controlling algae first requires understanding what makes it grow. Algae require certain nutrients to thrive. The predominant nutrients are nitrate and phosphate. These nutrients are the result of the processes of metabolism and decomposition, but can also be found in some salt mixes as well as tap water. Care should be taken when choosing a salt so that it does not contain either phosphate or nitrate. In the case of tap water if nitrate or phosphate are found to be present it may be necessary to use a method to remove them. To find out if they are present the tap water should be tested and you can ask your local water authority for a chemical read out of what is in your water. They will usually provide this information for free. Values for nitrate and phosphate should be as close to zero as possible.
The easiest methods for removing unwanted elements from water are either reverse osmosis or deionizers. Either of these systems adequately removes these unwanted compounds as well as heavy metals, and other undesirable substances so the choice is yours. The best systems contain both components to filter these nutrients out as well as sediment cartridges and carbon filters to help maintain the viability of the cartridges. The water that is produced by these units is very pure. These units have a high initial cost, but when their cost is considered for the years they will be in service the water they produce only costs pennies per gallon.
It is advisable to keep both nitrate and phosphate levels as low as possible, and preferably at zero. Even when one of these compounds gets out of balance a particular type of algae may begin to predominate. In my own system I have seen the following relationships between nutrient levels and algae growth. When phosphate levels are high relative to nitrate Bryopsis predominates. When nitrate is high relative to phosphate turf algae will predominate. Since no hobbyist is going to keep a bioload comparable to that of the ocean it is necessary to employ specific means for reducing nitrate and phosphate to keep algae under control. To reduce nitrate levels the use of denitrifying filters, mud refugia with Caulerpa, sulfur beds or deep sand beds or large water changes can be employed. Denitrifying filters have been used in the hobby for a considerable period of time. Either batch or continuous flow denitrification filters can significantly reduce nitrate levels. Basically these filters employ anaerobic bacteria to convert nitrate into nitrogen gas. These bacteria are kept in a chamber devoid of oxygen and are provided an energy source in the form of either alcohol or a sugar solution to nourish their activity. These units are somewhat tricky and temperamental, but they work quite well in keeping nitrate levels low when a high bioload is present. Other means for keeping nitrate levels low are also being employed on a much wider basis. The two most common of these are deep sand beds and external refugia containing mud and Caulerpa. These natural methods incorporate denitrifying bacteria within the confines of the tank and when designed properly and maintained can keep the nitrate levels near zero. The latest means for controlling nitrate is the use of sulfur based media on which the population of anaerobic bacteria feed. This system is just coming into use in the U.S., but it is rapidly gaining widespread usage in Europe as a result of it appearing to be quite simple to set up and use.
Unfortunately none of the methods for denitrification have much of an impact on phosphate removal, except possibly the iron-based mud filter. Phosphate is a problematic compound in that it is not only a nutrient for algae, but it also acts as an inhibitor for calcification, which inhibits coral growth. Phosphate is present in the aquarium in two forms: inorganic (orthophosphate) and organic. Unfortunately this latter form is difficult to measure with all but the most advanced phosphate test kits. In addition it may be consumed by algae as fast as it is released so even though a test kit measures a low level there may still be significant phosphate present. Therefore for most hobbyists a better means for determining if phosphate is present is to watch the growth of algae.
Fortunately there have been several new introductions of phosphate removing compounds that are dramatically superior to the older aluminum-based phosphate removing compounds of the past. These products are iron-based and have been released by several manufacturers. I have used several of these compounds in my own tanks and have also seen the data from several comparative studies. From my own experience and as a result of the findings of these studies RowaPhos is the phosphate removing I now use exclusively. This compound is a processed form of ferric oxide hydroxide. As a result of the activation process on this product which is patented and unique to this product, it can remove more phosphate on an equivalent weight basis and bring the levels of phosphate lower than can any other product on the market. In my own tanks it is the only product I have used that has kept the pest algae Bryopsis in check. It works so well that there is no evidence of Bryopsis in the tank despite a very high bioload and heavy feeding. It is easy to tell when the media is exhausted in that when this occurs tiny clumps of Bryopsis begin to reappear. As soon as this occurs the media is replaced and the Bryopsis dies off within a week or two, long before it becomes problematic.
As mentioned above keeping nutrient levels low starts at the beginning, as it is easier to keep them low from the start than it is to reduce them once they have gotten high. This starts with the live rock. It should not be immediately added to the tank, unless the waste material it produces can be easily removed, as some of the live material that is on the surface and deep within the rock will die off as a result of the trauma of shipping. So the first step is to allow this rock to “cure” so that the dead material can be removed and the resultant rock will not foul the tank. To “cure” the rock, it should be placed in a container, either the tank to be used or even a clean garbage can, where aged clean saltwater of the desired salinity has been prepared. The entire container should not receive strong illumination during this period and the water should be agitated with a powerhead or two. In addition, any dead material that is found on the rock should be removed either with tweezers or by blowing water over it with the powerhead or a bulb baster. Please note that during this time the rock may have a slight or strong odor of decomposition depending on how cured it was when purchased and how much material was on it. After a couple of weeks in this container a 20% water change should be undertaken to remove the detritus that has settled on the bottom. Also at this time a test for both ammonia and nitrite should be undertaken. If everything is going right both of these tests should show only moderate to zero levels of these compounds and nitrate levels will be off the scale. Once these levels have dropped to zero, usually two to four weeks later, and there is no longer any decomposition on the rock it is safe to use the live rock. Keeping light levels low during this period, and removing detritus as it builds up should keep the development of micro algae on this live rock kept to a minimum. In addition, by keeping light levels low there will be some coralline algae development. This is important in that where coralline algae grow other algaes usually cannot gain a foothold. At this point a large water change should be done to reduce the nitrate levels. Also the denitrification and phosphate removing equipment or resin should be hooked up at this time.
Mike Paletta is the author of The New Marine Aquarium and Ultimate Marine Aquariums. He has been in the hobby for over 15 years and has written numerous articles for Aquarium Fish Magazine, Tropical Fish Hobbyist and Aquarium Frontiers.