For those who are unfamiliar with algae scrubber theory, explain why growing algae in your aquarium is a good thing?

Growing algae in your aquarium or pond duplicates the biological processes of oceans, reefs, rivers, and lakes. Marine biologists already know, but most aquarists don't, that algae is what absorbs all the "bad" things out of the water. Algae then uses these "bad" things to make food (algae) for the base of the world's aquatic food chain. Essentially all life in the water then feed upon this, creating more "bad" things which are once again absorbed by the algae. This is part of the "microbial loop."

Even real reefs, which many people mistakenly think get constant natural "water changes" from the ocean, are actually filtered by a combination of micro and macro algae. This is why reefs are "nutrient poor." Once one animals makes ammonia it is almost instantly taken up by algal cells just millimeters away. And the shallower the reef is, the more the absorption is done by benthic attached macroalgae (seaweed) than by floating microalgae (phyto). The "bad" nutrients never have a chance to make it out to the open ocean, even though the water itself does.

Once this is understood, the thinking can then turn to what is important: speed. The speed that the algae absorb the bad nutrients and grow in size determines how fast the nutrients are removed from the water; this is what you know as "filtration." A tomato plant, for example, can have many things done to increase its rate of growth, but another way of looking at it is that the faster it grows, the faster that nutrients are removed from the soil and thus the soil is "filtered" faster. Algae scrubbers maximize the growth speed of algae just like you can maximize the growth speed of tomatoes.

Also of importance and interest is how you can feed your animals with the growth. No other filter can be fed to your animals like algae can. As a matter of fact, if you set your system up properly and choose the right number, size and type of animals, you will never have to feed again—it will all be self-feeding and self-filtering.

How did you get involved in algae scrubbing? Algae scrubbing has been around for over 20 years. Some designs required a lot of room and lighting to grow the algae. Other systems focused on raising algae in a refugium. None of them stood the test of time. What were the downsides of these designs?

In 2006 when I hired a fish guy to set up a 90 gallon reef in our office, I wanted him to do everything, even feeding. And he did—but within a few months everything was dead. So I found a new fish guy. He re-did everything but within a year everything was dead again. So I started reading Wet Web Media and then Reef Central and learned that both fish guys had no idea how things worked. So I continued reading and decided I wanted to have seahorses with live food that I grew, and I found out I needed lots of algae to feed the pods for these horses to eat.

Then I learned that algae does lots of filtering too, and in 2007 I wanted to have an algae device that could filter and grow pods too. Well I could not find a single algae filtering device for sale anywhere, not even used. So I searched for ones to build and only found the original dump-bucket design by Walter Adey which dumps water onto a screen and is described in his patent 4,333,263 from the year 1980, and also in his book Dynamic Aquaria.

As is turns out, the key to a fast rate of algal growth and nutrient removal from the water is a very thin air/water interface layer, similar to the thin laminar layer of air that touches a wing in flight. This layer of water does not move (is static) relative to the algae molecules, and thus it stops nutrient flow almost as if you turned off all the flow in your tank. Just increasing water flow across the algae does not help much because the static laminar flow is still there, like the non-moving air molecules touching a wing. However if you introduce air into the water, the water molecules are physically pushed aside which lets nutrients reach the algal cells, similar to if little vacuum bubbles flowed across a wing to break up the air molecules. Adey's dump-bucket provided this action by the agitation of the dumping water; flowing-rivers and waterfalls do it by the thin water layer.

The dump-bucket design had problems with complex unreliable moving parts, high cost, and the patent which turned out to cause trouble in the 1990's when others wanted to build and sell them. The flowing-river designs were also available in the 1990s but were marketed very little, took up lots of horizontal room, and were very costly even though there were no moving parts. And there were other even more complex designs that only a few people bought. So the idea faded.

Well I knew there had to be an easier way to get water across a screen in a way that did not take up a lot of room. So while half-asleep one day I came up with the idea of letting water flow down a vertical screen, which had no moving parts, took up no look-down room, and which had the added benefit of putting water and illumination on both sides of the screen. This important 2-sided action keeps the roots attached to the screen twice as long before the roots self-shaded, died, and let go thus losing the filtering; it cannot be done with the dump-bucket or the flowing-river designs. My waterfall design only needed a pipe and a screen, and it's the same design used now by almost everyone who wants a waterfall.

Refugiums are a different category and are not classified as a scrubber because they are so weak. They don't use any of the increased-growth-rate techniques that scrubbers do, and thus must be very big to match what filtering a scrubber can do. And if a refugium is on the same system that a scrubber is, the scrubber will usually kill and consume the nutrients from the refugium, because as far as the scrubber is concerned the macros in the refugium are just more weak nuisance algae that must be removed. Refugiums do grow lots of pods though, but so do scrubbers, and if you want to you can down-tune your scrubber so that you can have a refugium and scrubber together.

How are your scrubbers different than previous algae scrubber designs?

During another half-sleeping night while trying to improve the waterfall design, I came up with the upflowing bubble design which is now patent 9,115,008 and 9,708,207 as well as China utility model CN203392929U. The upflowing bubbles create the maximum air/water interface turbulence ("scrubbing bubbles") you can get because the inside of bubbles are "dry" and thus when a bubble physically rubs an algal cell the effective thickness of water on the cell is zero. So bubbles are theoretically more powerful filtering than a layer of flowing water, which on a waterfall is about 3 mm thick. More importantly for the typical aquarist, however, is that an upflow scrubber can be placed underwater; this means that it can go inside a sump, display, or pond, instead of above, and this eliminates all spills, overflows, water pipes, water pumps, and drain noises. These upflowing designs are called Upflow Algae Scrubbers (also UAS) and are only made by us, currently in the form of our HOG scrubbers, SURF, and DROP models.

Our upflow designs also don't spray water sideways like a waterfall pipe sometimes does when growth gets into the slot; this can spray onto wires and cause shorts in the sump. And our lights are either submersible, as on our SURF and DROP models, or located remotely in a protective shell, as with our HOG models, so there is no chance of water splashing onto the light or salt spray corroding the lights as occurs on waterfall scrubber lights. And speaking of lights, almost all light stays contained in our upflows, whereas many waterfalls let all the light out. Lastly, our upflows can go much longer before cleaning, if needed for vacations.

What are the differences between the Surf, Hog, and Drop models?

Our uplow designs all use a very rough algae attachment surface called Green Grabber® which is the same rock material that seaweed has learned to attach to at the beach; and since Green Grabber surfaces are bright white, it reflects the most light possible back to the algal "roots", thus reducing their self-shading effect and keeping the algae attached longer. All models also use airline tubing to bring air bubbles below the Green Grabber surfaces so that the bubbles can rise up and physically rub the rough surfaces. This physical rubbing is the important part because it removes the static laminar water layer mentioned above, and it also brings CO2 (in the air) to the algae. CO2 is how algae gets the carbon needed for growth. By pulling carbon from the CO2, less is pulled from the alkalinity in the water, and thus the pH of the water stays higher that if you did not have bubbles (refugiums and macro reactors can pull alk and pH down).

Our first upflow, the HOG (which stands for Hang On Glass), was first offered in 2012 and has a design patent D784629. Similar to HOB and HOT aquarium filters which save space, our HOG design puts LED lights on the outside of the glass, and the Green Grabber surfaces on the inside of the glass, and uses magnets to attach them together through the glass. This means you can slide the scrubber around on the glass, and also means that only air goes into the water; all electrics are on the dry side. By sliding it on the glass, it's easy to position it above or below the waterline, depending on if you want bubbles at the surface or not. And since some growth grows on the glass too, sliding it sideways allows you to feed your animals from the glass without having to reach into the water to remove the inside part. This is really neat for freshwater displays or for saltwater sumps that have animals. Some of the HOG models are available with strings too, which are 2-sided by nature and help fill up the inside area of the compartment in saltwater applications.

In 2013 we came out with our SURF model, and like it sounds, it surfs (floats) on the top of the water. It has the Green Grabber rocks in an internal compartment, along with 2-sided attachment strings, and bubbles come up from below. The lights act like a lid too, and are sealed in a very thick solid plastic which protects them from the water. Since SURF models are so thick and are surrounded by foam, they are the quietest of three model types; most people say their other equipment is the only thing they hear. SURF's are easy to harvest once they are growing thick, because you just lift the lid up and pull out algae. The strings really help fill up the inside compartment with growth; they are not for freshwater however because these same strings are harder to brush clean of the long thin slimy growth that you get in freshwater. SURF's are great for saltwater sumps, and even for sumpless displays if they won't block the display lights.

Also in 2013 we came out with the DROP, which is designed to drop down into the water and just stay there (no floating). The Green Grabber and bubbles are the same, and the larger ones also have strings for saltwater usage. DROP's are really great for the back of nano's because they drop right down into the small spaces, then lift right out so you can take them to your sink for cleaning/harvesting. DROP's are great for over crowded sumps when a HOG won't fit in the cabinet and a SURF has no room to float.

Explain how you tie feeding rates to the algae scrubber size and why this is unique?

Algae grow by absorbing "bad" things out of the water such as ammonia, ammonium, nitrite, nitrate, phosphate and metals, and not by pumping gallons of water. The bad things come from the food you feed after the food is consumed by the animals, and since the number of gallons of water does not change this, it makes sense to rate a scrubber based on how much you feed. It's kind of like rating a restaurant on how many people it can feed a day instead of how many square feet of space it has.

So if you have a 10 gallon nano or a 100 gallon system, if you only feed enough for one clownfish, then a small scrubber is going to work roughly the same in both cases. But if you are pouring a lot of food into a small tank, after the animals consume it there are going to be a lot of nutrients that will have to go somewhere, no matter what the number of gallons is. Nutrients in ("input") must equal nutrients out ("export"). Like a refrigerator, food in must equal food out. Other types of filters don't actually remove nutrients, or worse, they cause more nutrients, and so they rated on the number of gallons instead.

Some aquarists have had difficulty getting algae to grow in DIY scrubbers and refugiums. How have you overcome this with your scrubbers?

Putting refugiums aside for now, and like any piece of aquarium equipment, there is sometimes the particular occurrence of a tank where a DIY or purchased scrubber has "trouble". Usually after we see pictures of the growth, we can tell what needs to be done. Almost always it's a user who did not follow directions; remember you are trying to grow live organisms which do a neat function: out-compete nuisance organisms in your tank. And these organisms need a particular environment that the user sets up for the scrubber.

But even scrubbers that are not growing the "desired" super thick green hair algae will still export nutrients; matter of fact the darker the growth is, the more nutrients it contains per gram. It just needs to be cleaned more often which many people do not do. As far as design goes, our models maximize the attachment, lighting spectrum and strength, and turbulent air/water interfaces that allow for fastest growth and filtering.

We know algae scrubbing isn’t an instant fix. How quickly will the typical reef aquarium respond to a properly-sized scrubber?

If the goal is just to help reduce nutrients and glass cleaning, then a scrubber should be of help as soon as it gets growing good, which is usually 1 to 3 weeks. As the scrubber develops more, then the nutrients will drop even faster and the glass will need cleaning even less, up to a point. And of course the scrubber will be there and available if any pulses of ammonia occur such as with a dead fish or over feeding. However most people unfortunately get a scrubber later, when there is already a problem such as nuisance algae on the rocks. This usually occurs 9 to 18 months from a tank's set up, when the rocks have absorbed as much phosphate as they can hold. Now the scrubber must absorb ammonia from the animals eating, and also the phosphate from the rock; each 50 pounds of problem rock provides as much phosphate as feeding one frozen cube of food per day. So if sized and operated properly such that the amount of rock is considered, then the rock usually lets go of the nuisance algae in 3 to 6 months. This can be accelerated of course by using more scrubbers.

What kind of algae grows on the Green-Grabber surface? Is any type more desirable than others?

Algae, like moss or grass or trees, grow based on the environment. The Green Grabber rock textures are designed to hold on to green hair algae (which use enzymes to bore into the rock), and dark slime (by having lots of places to grab). But what's important to understand is that you don't tell it what type to grow; instead it grows based on the conditions. Yes you can control many conditions in a scrubber such a lighting and bubble flow, but most important are the nutrients in the water (ammonia, ammonium, nitrite, nitrate, phosphate, metals and CO2) that you are trying to filter. An enclosed scrubber such as our HOG, SURF and DROP models does alter the environment however, by re-circulating the water and nutrients inside the compartment, which in high nutrient water lets more nutrients be removed from the water before the water exits. Thus the water conditions inside our scrubbers can be "lower nutrient" than outside, which will allow them to grow greener, sooner, because higher nutrient water grows darker slime which has more proteins per gram of algae. By contrast, a non-recirculating scrubber such as a waterfall, has the same nutrients in and outside of the scrubber because there is no re-circulation.

How often should your scrubbers be harvested? What’s the best way to harvest algae without upsetting the system? Can I over-clean a scrubber?

When growing dark slime like many new scrubbers do, the scrubber should be taken to the sink and toothbrushed out as soon as you can't see the white rock surfaces anymore. This gets all the nutrients out of the water, and can be as often as every 3 days if there is a lot of phosphate in the rock, or if nutrients are high in the water, or if you feed a lot several times a day which will makes lots of ammonia. The Green Grabber surfaces hold on to the slime as well as can be expected, but slime has no roots and will get washed away fairly soon, so more-often cleaning really helps and also uncovers the Green Grabber rock surfaces so green hair algae can attach (green hair cannot attach through slime).

When green hair algae is growing, the "roots" of it will get into the Green Grabber rocks and hold on longer, so you can go 7 to 10 days before cleanings. 14 days is about as long as you would want to go because the self-shading of the growth will not let much more growth occur beyond that, and if it's not growing, it's not filtering as much. If needed, such as vacations etc, upflow scrubbers can be left uncleaned for a month or so because they are always underwater and the algal strands always move around and get some flow and light (it just does not filter much after 10 to 14 days). This is compared to waterfall scrubbers which cannot ever go past 14 days or so because the growth mats down and blocks all flow and light from reaching the roots, and the roots die and let go causing globs of growth to do down the drain.

You won't be able to remove all the green hair from the Green Grabber surfaces because of the strong attachment, so it's not really a concern that you would remove too much. But for strongest filtering, the idea is to only remove about half the growth so the remaining growth can still absorb nutrients and keep growing. Many people find that their scrubber is filtering so much that if they clean it completely, they get a rise in nutrients and their glass needs cleaning right away. A better option is to have two scrubbers, where you only clean one at a time; this leaves the other one fully growing and filtering. Two smaller scrubbers is always better than one larger one. You cannot "over scrub" though, so multiple scrubbers never hurts and are also there in case of ammonia spikes; the scrubbers will simply not grow as much if not needed. This is compared to chemicals which can over-filter and cause other problems. A scrubber however is just algae, and uses the same growth mechanisms that corals do, so it cannot pull nutrients too low.

Can a fast-growing algae scrubber replace a protein skimmer? Are skimmers and scrubbers compatible?

Skimmers are really not related to scrubbers. Scrubbers (algae) remove ammonia, ammonium, nitrite, nitrate, phosphate and metals and CO2, and saturate the water with oxygen from the photosynthesis, and can provide food to the animals too. Skimmers however don't remove any of these things, and take food (protein) away from the animals instead. In particular, skimmers don't remove any ammonia/urea that comes from fish, which is of primary concern because it is what causes growth on your glass and what occurs when things die. However if you need to remove food particles from the water such as in a LFS display with big show fish, then you will need a skimmer. But if you want the water to have lots of food particles to feed the corals (especially at night) and small fish like real reefs do, then you will not want a skimmer. Skimmers and scrubbers can certainly be on the same system though, since one does not really affect the other.