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Algal Turf Filtration 101 Algal Turf Filtration is one of the most heavily debated topics in the reef aquarium hobby from time to time. I’ve read several arguments on the web over the years as it seems to start catching on only to be beaten back down each time. I use a turf filter on my reef aquarium and have participated in and created a forum thread on the topic. As I have stated previously, it is my belief that every common nutrient control method used today is viable given proper design, setup and husbandry practices. In addition to Berlin, Deep Sand Bed, Jaubert Monaco, Denitrators and Carbon Dosing I would like to present Algal Turf Filtration to my fellow novices in the hobby as an effective nutrient control method. Let’s start with a basic description of an Algal Turf Filter. Despite differing designs, they all have this in common. Aquarium water is made to flow over a grid that algae are cultured upon. The grid is illuminated to promote photosynthesis and absorption of nutrients such as Nitrogen (Ammonia, Nitrite and Nitrate) and Phosphorus (Phosphate). The most common algae species on the grid are the same as we consider nuisance algae in the aquarium.
Dr. Walter Adey is credited with pioneering the use of turf algae as a filtration medium at the Smithsonian Institution’s Natural History Museum in the 1970’s. Dr. Adey and Karen Loveland published “Dynamic Aquaria-Building Living Ecosystems” first edition in 1991. Their book is about creating a complete ecosystem and includes the use of turf algae for filtration and nutrient recycling in an attempt to replicate nature in an enclosed environment. The use of protein skimming, activated carbon and ozone were discouraged. It should be noted that using turf filtration in home aquaria is typically different than what Dr. Adey did at the Smithsonian. · Dr. Adey essentially closed his system from almost all import and export and simply transferred the algal mass/energy back to the aquarium as needed1. · Most hobbyists add substantial amounts of nutrient over time and harvest and discard the algae for nutrient export (personal observation). Benefits of Algal Turf Filtration The primary benefits of turf filtration are similar in nature to that of using macroalgae as a means of filtration. Due to turf algae being more efficient at absorption than macroalgae due to photosynthesis taking place in more of the turf algae structure, it can be argued that Algal Turf Filtration is more efficient at some of the aspects they have in common2. Nutrient export is one of the key elements that interest most aquarists. A well covered turf algae screen is capable of absorbing 0.3 to 1.2 grams of Nitrogen per square meter per day1. Absorption rates for Phosphorus are not available, but absorption and control of Phosphorus is widely accepted. Turf algae absorb heavy metals such as lead, mercury, copper and zinc1. Turf algae maintain oxygen levels at near saturation levels while reducing dissolved CO2 levels in the water. Coupled with illumination of the turf filter while the aquarium is dark (Reverse Daylight Photosynthesis or RDP) a turf filter will help maintain pH while the aquarium is dark 1. Turf filters provide a refugium for zooplankton. The offspring of the zooplankton living in the turf filter provide a source of food in the aquarium as they are swept from the turf filter1. When I harvest my filter there are always numerous organisms living in the algae including pods, brittle stars and various worms. The species of algae grown tend to represent the excess nutrients in the aquarium. Several species of algae tend to colonize a turf filter. As a turf filter matures and the nutrients are absorbed, the dominant species of algae will shift as the quality of the water changes. A spike in Silica levels, for instance, would lead to a dominance of diatoms. When the excess silica is consumed and the diatoms are harvested the silica is removed from the system. Algal Turf Filters allow you to efficiently export nutrients in solid form. The increased density of nutrients can minimize the amount of water changes necessary due solely to nutrient control. If you have herbivorous animals you can feed them from your harvest and reuse the nutrients repeatedly. This can be used to reduce the amount of nutrients you import. Reported Drawbacks of Algal Turf Filtration As with many husbandry methods in our hobby, Algal Turf Filtration is not without its drawbacks. It’s my opinion that the factors which provide the benefits of turf filtration also contribute to its drawbacks. Leachates from turf algae can discolor the water to the extent that some corals may not receive the light they need to thrive due to absorption of the blue spectrum of light. Yellow water is one of the biggest negative observations made about Algal Turf Filtration2. As of 1998 Morgan Lidster of Inland Aquatics had maintained several reef aquariums for many years solely with Algal Turf Filtration with thriving SPS colonies in contradiction to common perceptions and observations, he maintained that the discoloration observed was due to improper maintenance3. To the best of my knowledge Mr. Lidster still maintains thriving reef aquaria with turf being the sole means of filtration. There are other factors that will affect the color of aquarium water and the contribution of algal leachates may be variable from aquarium to aquarium. The superior absorption capability of turf algae may lead to depletion of trace elements to very low levels. This factor would be more apparent when the absorbed trace elements are discarded in the harvested algae. Turf algae may be too competitive. This is completely anecdotal, but when I decreased the photoperiod on my turf filter the growth rate of my corals and clam improved. The Zooxanthellae in photosynthetic corals and Tridacna clams are algae as well. As they use Nitrogen, Phosphorus and Carbon as a food source, a certain amount is beneficial and overuse of turf filtration may deplete these nutrients to too low a level. Mitigation of the drawbacks All of these drawbacks can be managed. The good news is that most can be managed with common husbandry practices. The discoloration of the water can be managed with minimal protein skimming and the use of Granular Activated Carbon2 (and personal observation). The use of ozone dosing is also reported to maintain water clarity2. Depletion of trace elements can be managed with regular supplements. Minimal amounts of Nitrogen, Phosphorus and Carbon can be maintained by adjusting the photoperiod of the turf filter to a happy medium between control of nuisance algae and health of corals and clams (personal observation). Algal Turf Filter design considerations Grid size- Dr Adey cites grid size of the algal turf filters he used in his study. The home reef aquarium uses 3.8 cm2/liter of system water1. This calculates out to approximately 2.5 in2/gallon for us non-metric folks. He also recommends adding 20 to 30% in surface area if in doubt1. Lacking a doctorate degree I would consider 3.25 in2/gallon a conservative size with all other design features equal. Oscillating flow- Dr Adey suggests the water not continuously flow in one direction in the turf filter. The action of waves across the algae evenly illuminates the entire structure of the algae as well as providing increased gas exchange from the algae to the aquarium water. Several methods are suggested but the two most common are dump buckets and a teeter totter design. Dr. Adey indicated that without wave action that the production of oxygen in the turf filter was decreased by 50%1. Given this data and my aversion to another mechanism breaking down, my advice would be to increase the size of the grid to 6.5 in2/gallon. Flow rate- Dr Adey cites 3 to 10 GPM or 180 to 600 GPH depending on filter size1. My filter runs about 150 GPH with no problems. Light intensity- Dr Adey cites 1670Watts/meter2 on the same system he cited area for1. For you and me, that’s 1.07watts/in2. With the increases we added above removed for area due to lack of waves that would be about 0.37 watts/in2. Photoperiod- Dr Adey cites 10 to 18 hours a day for photoperiod on a turf filter1. My turf filter lights come on one hour before the aquarium lights go out and remain on one hour after aquarium lights come on. This results in 14 hours a day. I adjust the photoperiod on occasion when it seems warranted. Spectrum of light is not specified in my references, but as natural daylight is considered to be about 6500K and the water over the turf algae is shallow, I would suggest daylight or 6500K bulbs for the lights. My turf filter seems effective as used. At 50 gallons system capacity, approximately 288 in2, and 96 watts of light I have 5.76 in2/gallon in area and 0.33 watts/in2 in light. It is somewhere near the ballpark given Dr. Adey’s suggestions with the fudge factors. Algal Turf Filter Maintenance Harvest- I’ve read several articles, books and threads with periodicities ranging from 7 to 21 days between harvests. All accounts agree that algal production slow down when harvests are not conducted regularly. The tissue at the base of the algae will not receive enough light if the turf is overgrown. I would surmise that as the basal tissue breaks down that it may increase the release of algal leachates that stain the water. In addition to decrease in algal productivity, harvesting regularly will keep the zooplankton population in check. If left un-harvested the zooplankton population will increase beyond useable levels. I harvest 50% of my algae about once a month. This would also include removing any coincidental algae that may have grown on other filter surfaces that would block any light from the grids. Recommended harvest procedure: 1. Stop water flow through the turf filter. 2. Remove grid screens. 3. Scrape most but not all of the algae from the grids, stop and stare at all the pods, brittle stars living in there.
4. Clean the filter housing, check mechanical equipment as necessary. 5. Replace grid screens. 6. Start water flow through the filter. Bulb replacement- My PC bulbs have been in operation for over 3 years and I have yet to notice any detrimental effects from the expected spectrum shift. I would recommend trial and error rather than setting a periodicity. My two cents Some die hard adherents to turf filters seem to forget that the reefs have live sand and rock too. Dr. Adey maintains that turf algae is abundant on reefs and is constantly grazed upon1. There is no reason in my opinion to limit bacterial function in a Berlin, Deep Sand Bed or Jaubert Monaco system. These methods can work well in harmony and replicate nature more closely in my opinion. If a turf filter was added to one of the systems mentioned above, I believe it could be made much smaller than calculated earlier along with corresponding reductions in light and flow requirements. I use a small protein skimmer and activated carbon. I would not operate my turf filter without them. I have several species of hard coral, both LPS and SPS and every one of them is doing well. At the least, I would advise keeping them on hand if needed.
Have you heard the one about algae migrating from the turf filter to the aquarium? I’ve heard it, mostly in the form of a question to be honest. In over three years on my reef aquarium and seven previous years of fresh water use, I have yet to see this and I use no mechanical filtration at all. Those of you who know me have probably figured out that Dynamic Aquaria has been a major influence on the opinions I have formed over time. I am a firm believer that anything that makes my aquarium more similar to nature is a very good thing. I’m not selling turf filters, nor am I receiving money for expressing these views. There are some folks out there making and using small DIY turf filters. They seem very easy to build and inexpensive. My only reservation in following some of these novel designs would be maintaining some separation between the water and the lamps. Saltwater is very conductive. The proof is in the pudding Here are some recent photos of my aquarium and some SPS corals:
In closing I hope this article provided a basic understanding of Algal Turf Filtration and how it works. I still believe that other methods of nutrient control are just as viable (I’m sitting next to a cycling Berlin system) and urge each of you to use the method that suits you. This article has been a few months coming and it’s a big relief to write it. Thanks for your time. Happy Reefing References: 1. “Dynamic Aquaria- Building Living Ecosystems” Second Edition by Walter Adey and Karen Loveland published by Academic Press 1998 2. “The Reef Aquarium” by J Charles Delbeek and Julian Sprung published by Ricordea Publishing 1994, 1997, 2005 3. http://www.reefs.org/library/talklog/m_lidster_100498.html By Morgan Lidster of Inland Aquaria 10/04/98 Copyright MarineAquariumMonthly.com 2009. All rights reserved.
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