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Related Articles: The Complete Guide to Algae Turf Scrubbers: Part 1 by Santa Monica FiltrationMarine Filtration, Mechanical, Physical, Chemical, Algae Control, Nutrient Control and ExportMarine Set-Up, An Introduction to Reef Systems, Refugiums, Reef FiltrationMarine System PlumbingMarine Aquarium Set-Up Moving AquariumsMarine Biotope, Marine Landscaping

 Algae  Scrubber  


By Bryan, "Santa Monica", www.AlgaeScrubber.net  


Algae maintain water quality in oceans and lakes, and algae form the base of aquatic food chains as well. Wherever there is light and water, algae will find a way to grow, and aquarists often see algae as a pest. But instead of fighting it, why not harness its potential? Algae scrubbers restrict algal growth to within the sump rather than the main aquarium, and in doing so not only eliminate problems with unsightly algae smothering rocks and plants, but also serve to improve water quality in a variety of ways.

As they grow algae absorb ammonia, ammonium, inorganic nitrate, inorganic phosphate, nitrite, metals (including copper), and carbon dioxide. Algae also raise pH and add oxygen, carbohydrates, vitamins, proteins, enzymes, lipids, and amino acids to the water. Last but not least algal turfs are important habitats for tiny invertebrates such as copepods that drift into the main aquarium where they may be eaten by fish and other livestock, a particularly useful feature in reef tanks.

In short, algae scrubbers allow algae will do exactly what they do in oceans and lakes, improving water quality and environmental conditions. And yes, algae scrubbers work in both fresh and saltwater aquaria.

It's important to remember that algae such as these kelp play an important role in maintaining healthy marine ecosystems. BobF pic.


Algae scrubbers were invented in the 1970s by Dr. Walter Adey, who at the time was managing the aquatics department at the Smithsonian Institution. He called his device an algae turf scrubber or ATS, and this name is still used by many people today. Adey patented a design that uses a bucket to periodically pour water onto a screen, but he never tried to sell this design to the public. He let a few other people sell them, but the designs were expensive, noisy, unreliable, and had a lot of spray and salt creep. Because of all this, sales ended by the late 1990s, and since the designs were very hard to build yourself, nobody tried.

In August 2008, however, it was discovered that you can make simple, cheap and quiet algae scrubbers using PVC pipe and knitting screen. Thousands of people have since made their own algae scrubbers, and these have usually eliminated nuisance algae in their tanks within eight weeks. It's simple: the more algae that grow on the algae scrubber, the less that grow in your tank!


To determine the size of the screen and the lights, first determine the volume of your complete aquarium (including the sump, if it contains livestock) in gallons or liters. The wattage you end up using will be the total of the all the bulbs on both sides of the screen. The area of the screen will be width X height, i.e., a screen that is 10 X 10 has an area of 100, not 200. Here are the guidelines:

Use 0.5 actual (not equivalent) fluorescent watts total per gallon minimum [0.13 watts per liter].

Use 1.0 actual (not equivalent) fluorescent watts total per gallon for high filtering [0.26 watts per liter].

Make the screen 1.0 square inches per gallon, with bulbs on both sides (10 x 10 = 100 square inches = 100 gal)  [1.64 square cm per liter]

Flow is 35 gph per inch of slot length [60 lph per cm]. This assumes the slot is 1/8" (3 mm) wide.

Here a piece of 3/4" PVC pipe is being cut to size using a small power tool. "Santa Monica" Bryan pic.


A basic algae scrubber starts out with a ¾" (1.88 cm) PVC pipe, with a 1/8" (3 mm) slot cut along the length of it (the slot is only on one side; it does not go through to the other side). Mark the slot with a marker, and cut it with a Dremel tool.

Cutting this slot is actually the only hard part of building an algae scrubber. If you don't think you can do it, just ask another hobbyist to do it for you; a cabinet maker or model builder could also do it. It will probably take a few tries, so give yourself some time and some extra PVC to get  it right. As a last resort, you could try using a drill to make a series of 1/8" holes really close together, and then use a file to open them all up into a slot.

Next, get a piece of plastic canvas (otherwise knows as knitting screen) at your local sewing or crafts store, or online.  Rough it up really good with a hole saw from your hardware store. If you can't get a hole saw, then scrape a wood-saw blade sideways across the screen. A rough screen is very important; the amount of filtering a scrubber can do is proportional to how much the screen can hold on to the algae, without the algae being washed away. Spend some time making every part of the screen super rough, like a cactus. Tilting the hole-saw will help. Make the first pass in one direction, then do another direction. Repeat in other directions. When roughing the edges, go outwards. Be careful on the other side of the screen, since it will rip more easily than the first side. If you do rip a small piece, the screen will still work fine.  Do not ever use a smooth non-roughed screen; the algae will fall right off and you will have no filtering.

Now slip the screen into the slot, and attach it with zip-ties wrapped around the pipe. The bottom of the screen should go into the sump water an inch or so, to keep the flow quiet and bubble-free.

Use a hole saw like this one or a wood saw blade to abrade some plastic canvas (the grid-like sheet in the background) both up and down and side to side. This will produce a textured screen coarse enough to provide a good surface for a thick algal turf.  "Santa Monica" Bryan pic.

The finished sheet should be very rough, but be sure to keep the top part smooth so that it fits into the slot you cut in the PVC pipe (shown below).  "Santa Monica" Bryan pix.

Installation and maintenance

Lights. Attach your lights on both sides, and point them to the middle of the screen. The bulbs should be about 4" (10cm) from the screen. Simple CFL (compact fluorescent) bulbs with clip-on sockets work fine. Get the bulbs that say 'warm' or 'soft'. Put the bulbs on a timer, so that they are on for 18 hours a day, and off for 6 hours. Never let the bulbs run 24 hours, because you will get no filtering. Lastly, larger screens should have more bulbs, so the screen gets an even amount of light across them.

Now connect your pump (or overflow) to the pipe (the water should flow 24 hours), and wait for the growth! You should  start seeing improvements in your tank after you have cleaned off about four full screens of algae.

Weekly Cleanings. Every 7 days, you need to turn the flow off and remove the screen. Take the screen to your sink, and remove most of the algae. Leave some algae on the screen, so that it can still filter, and so it will grow back quickly. Your first or second week might not grow too much, especially if you are not feeding much (like on a new tank), but later on it will fill in faster.

Sometimes, however, it will starting growing dark, thick algae right away, which looks like oil. This happens when the nitrate and phosphate in your tank are very high. If your scrubber is powerful enough (strong lights, fast flow, and high roughness on the screen), then it may start growing green after a few more days, and be mostly green by the end of the week. But if your scrubber is not powerful enough, and it never starts growing green, then you'll need to clean the dark stuff off before 7 days. This is because the dark algae block the light from reaching the bottom algae layers. So if the screen stays dark, clean it every 3 days until it starts turning a lighter brown. After that, switch to 5 days until it starts growing green. Once it starts growing green, switch to 7 days from that point on.

The biggest mistake people make when running a new scrubber is not cleaning every 7 days. If you wait longer than this, the pods (in saltwater tanks) start eating too much of the algae, and this puts nitrate and phosphate back into the water, thus reducing the filtering. And for both saltwater and freshwater, waiting longer than 7 days causes too much algae to grow on the screen, and it starts breaking off and going into your tank. This doesn't hurt anything, of course, since it's just algae, but it still puts nitrate and phosphate back into your tank, which defeats the purpose of the scrubber in the first place. So just clean every 7 days and it will be fine.

Types of algal growth

When new screens start out, they almost always just have a light brown coating of slimy algae. The second week, it usually gets darker, and by the fourth week it can get pretty thick. It's important to realize that all algae remove nutrients (nitrate and phosphate) from your tank, so any algae that grows on your screen is algae that can't grow in your tank. As the nutrients in your tank come down, the type of growth on the screen will change. Here are some different types of growth:

Light Brown Slime: New screens, and sometimes older screens the day after they are cleaned. Perfectly normal.

Black Oil/Tar: Very high nutrients in tank. Screen must be cleaned every 3 days until growth is not so dark.

Green Dust/Specs: There are silicates in the tank, possibly coming from the sand. This growth does not filter well because the particles will let go into the tank where they color the water green. If this growth does not change into a better type of growth, you many need to replace your sand with a type that does not leak silicates. This is very rare, however.

Green Spaghetti/Sponge: This is the best type of growth, because the light-green color and open structure allow light and water to penetrate through all parts of the algae. Also, it is firm and compact, like a sponge or Chaeto, and will not let-go and clog drains easily.

Long Thin Green Hair: This types occurs mostly in freshwater, and filters a lot because the light and flow go throughout the algae. But depending on how you build your scrubber, the strands may get so long they break off. Adding a bit of Mono Potassium Phosphate to the water, to increase the phosphate, should fix this and make it growth thicker.

Yellow Rubber: Your flow is too low, and is not delivering enough iron to the algae. If you can't increase the flow, then move the bulbs further back. If you can't do that, then run the bulbs a few hours less each day. You can also try adding iron to the water, such as Kent's Iron and Manganese.

Cyano: Your flow is too low.

Big Bald Spot In Middle: Your flow is too low, near the light. If you can't increase the flow, then move the bulbs further back. If you can't do that, then run the bulbs a few hours less each day, or get smaller bulbs.

Mysteriously Appearing Small Bald Spots: If the spots are circular, and the algae is a thin film, then these are pods eating the algae. Your scrubber is just not powerful enough to cover them with thick growth in 7 days. If the growth is thick, however, and the spots are irregular shapes, then the algae is letting go from the screen. Your screen needs to be rougher. If you can't do that, then either reduce the flow, or clean more often, so it does not get so thick and heavy.


This DIY simple scrubber is meant to be used in normal sumps which sit under the tank If you don't have a sump, or if you have a nano with a sump in the back, then it gets more complicated, and will require more research on your part before attempting to build a suitable scrubber.

For more detailed information, or to ask questions, go to AlgaeScrubber.Net . You now have all the info you need to build yourself a super simple and cheap filter, and say goodbye to the nuisance algae in your tank!

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