Intermediate Topic Building Your Own Algal Turf Scrubber (ATS)

Instructions on how to build your own Algal Turf Scrubber or ATS.
  1. I’ve been keeping reef aquaria for a very long time. My first reef tank, softies and zoanthids, was set up around 1987. What folks newer to the hobby may not appreciate is the dearth of equipment choices that was available to us back then.

    I built my first skimmer, not because I wanted to, but because the commercial options were so limited. There were no wavemakers, precious few lighting options, and certainly no algae scrubbers. We were forced to be resourceful, and do-it-yourself was often the sole recourse. So, I got good at it, and discovered along the way that it was fun to build your own stuff.

    I was also a voracious reader and bought almost all of the reef aquarium-related books that were available (most I still have). Some were better than others, but one, published in 1991 really caught my eye. Written by Dr. Walter Adey, then of the Smithsonian in DC, Dynamic Aquaria chronicled his journey with algal turf scrubbers (ATS) as a different way to control nutrients in aquatic systems.

    I immediately set about making one. His then design, which I essentially replicated, was to build a large trough with a screen on the bottom and a dump bucket at one end. Lit with appropriate lights (then HID of some kind), the periodic surge of water from the dump bucket across the screen would encourage turf algae growth.

    First Algal Turf Scrubber.
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    Photos are courtesy of Simon Ellis, ©2019, All Rights Reserved.

    It worked really well, and along with my skimmer and the continuous use of GAC, I was able to maintain very low nutrient levels without any negative effects. But it was large, noisy, messy, and expensive to run; and since I had made it out of epoxy-coated plywood, the box invariably started to ooze. So, I worked on different designs, some better and some worse, until I stumbled upon one that I really liked. Not my own certainly, but a design that most now call the waterfall ATS.

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    Photos are courtesy of Simon Ellis, ©2019, All Rights Reserved.

    Fast forward to 2018. I have been running a 12”x12” double sided waterfall ATS since 2013. I built it myself out of acrylic and it is fed from one of the siphon drains on my tank. It is lit by a pair of now discontinued ReefBreeders LED Fuge lights, and it has performed very well even if it makes the entire sump room look pink. Scrubbers are typically sized based on the number of food cube equivalents they can support, but as my display now boasts 400 net gallons and over 120 fish the scrubber is too small.

    Here, then, is my process of building a bigger unit. Before I detail the process, I will say that good commercial sources now exist for an ATS. I’ve not personally used any of them, but they seem quite credible. I’m building mine because I enjoy making things and because I needed one that exceeds the size of the commercial options.

    The ATS is a pretty simple device. You need a screen on which the algae can grow, a way to feed it tank water, and a light source. I see many folks that just hang a screen in their sump, but I personally prefer a containment box for the screen to keep splash and aerosolized salt spray to a minimum. My new scrubber will be 23” long by 20” tall by 4” wide. The screen area will be slightly more than double that of my older unit.
    Unless somebody feels the desire to go ‘old-school’ with a dump-bucket-style scrubber, the waterfall design really is the best approach in my view. The box to contain the screen can be made from plastic (usually acrylic) or from glass. I have no real preference for one over the other. This time I decided to use glass simply because I did not have any acrylic sheet on hand and the local glass shop owner is always happy to indulge my requests for odd-sized pieces. The scrubber box is not required to withstand any real pressures, so ¼” plate glass with polished edges is quite sufficient.

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    Photos are courtesy of Simon Ellis, ©2019, All Rights Reserved.

    Assembling the box isn’t particularly difficult, just ensure at least a week for the silicone to properly cure. I use silicone that is sold as ‘aquarium silicone’. Probably it’s just the same as you could buy at the home improvement store--just make sure to get acetoxy cure (like GE1) as it works better on glass, even though the vinegar smell is a bit tiresome. I’m alright with spending a few extra dollars for the branded stuff.

    A caulking gun, some blue painter’s tape, a couple of diamond hole saws, and a bit of patience. I ground a hole in the bottom glass for a 1 ½” bulkhead fitting (this scrubber will be fed about 600 GPH) to drain water from the unit; and a second hole in the top of one side for a 1” bulkhead for the feed water. Note the two small pieces of glass supporting the ends of the feed bar. Once laden with turf algae, the bar can sag so supports are advisable.

    Usually I would do this kind of thing in my workshop. However, my workshop is an unheated space, and I was concerned that the silicone would not properly cure, so, I temporarily repurposed the dining room. Never gets used for actual dining anyhow.

    Perhaps the trickiest part of the entire build is the feed bar. I prefer a T-bar that feeds water from the center but feeding from one end (like most of the commercial units) is satisfactory. I prefer center feed because it tends to better equalize flow along the length of the bar. Essentially, the feed bar is a 1” PVC tee fitting with two lengths of capped 1” pipe out of each end. That part is easy, but cutting the flow slot can be a challenge, particularly if you don’t have the proper tools. I did not clearly recall how I had done this back in 2013, so initially decided to use a hand-held router with a wooden jig. Apparently that’s NOT how I did it! Either my hand was steadier back then, or I used the table saw.

    Always buy extra PVC fittings, just in case. Using the table saw to cut the groove worked a lot better. You just need to jam a few shims into the groove when solvent welding the pipes into the fittings, otherwise the slot causes the pipe to close up. I then used a small saw to extend the groove into the T fitting.

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    Photos are courtesy of Simon Ellis, ©2019, All Rights Reserved.
    The screen on which the turf algae will grow must slot into this groove. The screen material that I prefer to use is sold online as plastic ‘canvas’; it’s basically a semi-rigid, plastic mesh used in arts and crafts projects.

    Some ATS designs I have seen use zip ties to hold the screen in the slot, but I prefer clips. Basically, I just cut thin rings of 1 ¼” PVC, remove a small piece and clip them over the feed bar. You can rotate them through perforations in the top of the screen to hold the screen in place.

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    Photos are courtesy of Simon Ellis, ©2019, All Rights Reserved.
    In this particular unit, since I could not find sheets big enough, I’m simply using a split screen, with two equally sized pieces on each side of the bar. I suggest that you use rough sandpaper to roughen up the plastic screen material--it allows the turf algae to gain a better hold.

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    Photos are courtesy of Simon Ellis, ©2019, All Rights Reserved.
    Now that the box is assembled and siliconed with the requisite bulkheads, and the feed bar is in place with the screen sections hanging down, it is time to consider lighting. In the picture, the two sides of the screen are not entirely symmetrical. I will fix that before it's finished. Happily, I ordered a bunch of the screen material to account for faux cuts. I neglected to get a piece of glass for a lid, which I do recommend. I don’t worry too much about clean silicone joints as long as the box is structurally sound and water tight. Within a few weeks of hooking this up, it’ll be all gummed up with algae anyhow so who really cares about a little sloppy silicone.

    Lighting is an individual choice; though I do prefer the horticultural/grow light options available online. Obviously, it depends upon the size of the unit and whether you care about light spill or not. In my case, the ATS goes into the sump room so I don’t worry about light containment. I did think briefly about using a pair of Kessil H380 lights, but the cost was not appealing, and I thought that hot spotting would likely be a problem. I think a LED panel light is probably best for most implementations.

    As I noted above, my current ATS uses PAR38 LED bulbs, but they weren’t going to be big enough for this larger unit (plus they’ve developed a bit of a flicker lately). While there are a bewildering array of LED grow lights available online, be wary of really cheap fixtures. You usually get what you pay for, and some I have bought failed very quickly. This time, I decided to go with a Growstar 300 watt on one side (where I have a lot of space) and a 150 on the other (where space is limited). The reviews on both were pretty good--plus a friend of mine in Colorado uses them to grow his ‘tomatoes’ and has found them to work pretty well.

    Just keep in mind that these grow lights are ‘sized’ based on traditional equivalence. In other words, the 300-watt light generates PAR equivalent to an older 300-watt HID light, but only draws about 115 watts. The stand for the light in the picture is temporary – I just wanted to get a sense of the distance I’d need to get proper coverage. If you are space limited a square panel would probably work better.

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    Photos are courtesy of Simon Ellis, ©2019, All Rights Reserved.
    I will keep a small mag-cleaner on each of the main panels to more easily keep the glass clean. Otherwise, that’s essentially it. The box will need to cure for a full week, at which point I will be able to press it into service. I will keep the old scrubber in the system while the screen on this new unit seeds. Once that happens ‘out with the old’.

    Happy to entertain any questions or comments, and I will post a picture of it once installed.

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    Note from the Editor: The original Algal Turf Scrubber was invented and patented by Dr. Walter Adey in the late 1970's, and its design included a surge bucket, which Simon mentions. In today's reef vocabulary, ATS or algae scrubber has come to mean a scrubber of any design that performs the same function, in the same way that Kleenex means tissue or Band-Aid means adhesive bandage even though those are actually brand names.

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    Author Profile: Simon Ellis, who is ca1ore on the forum.

    Simon Ellis lives in Stamford, CT. He has been keeping reef tanks since 1987, with a short break in the 20-teens. When he went to the very first MACNA meeting, Albert Theil introduced him to the technology side of reefing. He always thinks of himself as a fish-first reefer, though he does admire large coral colonies.

    He is gradually getting larger and larger systems. He currently has a 450-gallon display tank with another 200-gallons of connected tanks. He's always thinking about the next tank; "450 is too small after all." His next project is 1,200-1,600 gallons.

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