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Algae Scrubber Basics 1 of 14

Posted 02/19/2012 at 09:28 AM by Floyd R Turbo


In the past 6 months, there have been several basic changes to the core concept of the Algae Scrubber, and these changes resulted in many people experiencing better growth and more effective filtration.

By far the biggest change is that the size of the screen needed for a given system is no longer dictated by the volume of the tank or the bio-load, but is instead based on the amount of food you add to the system. This has resulted in much smaller screen requirements; in some cases, ridiculously small screens when compared to the previously guidelines.

The second is the optional lighting scenario using twice the light intensity and half the photoperiod, which can power through the initial dark algae growth stages some experience, and can also be helpful in battling tough tank algae.

Third covers the advent of LED Algae Scrubbers.

I went through and edited the previously posted “Basics”, mainly for the purpose of addressing the 3 above items. Many other sections were also affected, and I have incorporated as many hints, tips, and tricks as I could. Even if you have read through the previous “Basics” summary before, read this one again. And again.

Some of the pictures in this are based on the old sizing requirements, but are still good for examples of specific principles. For this reason, and the lack of pictures of smaller builds using the new requirements, I have kept many of the pictures the same.

Part 2? Yeah yeah…I incorporated a little more into this one, and I have a start on Part 2, but it needs revamping too!

This will likely be the last summary revision for this version of the Algae Scrubber. There is a new version being developed (not by me) and it is currently being kept under wraps as it is in the middle of the patent process (again, not by me) so I know very little about it, except that it will supposedly have vast improvements in many areas, and will not resemble any Algae Scrubber that anyone has ever seen (this frustratingly includes me). The principles are all the same, so this summary has value still. But just be aware that a lot of this information (that I’ve but so much time into assembling…grrr!) might just get thrown out the window. Tidbits of info? On the new version, you won’t have to cut a slot in a pipe, can remove and clean the screen without shutting off flow,

Anyways….the re-revamped Basics:

Algae Scrubber Basics Summary: February 2012

There are many options when it comes to building your own Algae Scrubber. Hopefully this series of posts will wrap up all the basic concepts as clearly and concisely as possible. It seems that many people look at this concept and think they can make some kind of major improvement, and post their idea. Then, a newbie can look at that and think that it makes great sense and mimic it, without understanding the pitfalls. I feel that it is important to understand the concept and purpose behind the basics, and why you should rarely deviate from them without fully understanding the basic concepts first.

Most of the issues people encounter with their DIY builds can be directly attributed to missing one or two of the basic principles. So consider this a "best practice" summary. That is, there are several ways to build an Algae Scrubber, but there is always a cheap and easy way, as well as the most effective and efficient way.

The Vertical Waterfall Algae Scrubber

99% of this summary is dedicated to the basic of designing and constructing a modern, vertical screen, waterfall-style Algae Scrubber, illuminated from both sides. This is simply because this design is currently by far the most efficient and effective type of Algae Scrubber design, and the only one that I recommend building. The occasional mention is made regarding considerations to make for building a single-sided Algae Scrubber, or for a horizontal/slanted Algae Scrubber. From here forward in this series of posts, horizontal or slanted Algae Scrubbers will be referred to as “non-vertical”.

The vertical waterfall style Algae Scrubber is very efficient for a couple of reasons. The design allows you to illuminate the algae from both sides and place the lights very close, which reduces the distance that light has to travel through water in order to reach the algae. The water flow over the screen is relatively thin and moves fast; this is important, because algae requires turbulent flow in order for nutrients to reach the cells on a microscopic level (Google “boundary layer”). Because of both of these factors, vertical Algae Scrubbers require less light and material than the older style non-vertical Algae Scrubbers for equivalent filtration capacity.

The Slot Pipe, Screen, and Fasteners

The principal component of the modern vertical waterfall Algae Scrubber is the slot pipe and plastic canvas screen. The screen is inserted into a section of horizontal PVC pipe which has a slot cut into it. The screen is typically held in place with a fastener through a cut-out section of the screen, like this:

Slot Pipe

The slot pipe itself should be Schedule 40 PVC at a minimum. Don't use vent pipe, flexible hose, or thin-walled PVC. The reason is that cutting a slot in the tube weakens it enough that it can bow over time and cause the slot to change width, and cinching zip ties tightly around it can make that worse. This is especially true for a wide, tall Algae Scrubber. Anything over 24" should probably have 2 slots, with a small section in the center left uncut (maybe 1/4") with some kind of means of support at the center. It may look fine at first, but with heavy growth, you start to see this:

I'm not saying that it won't work, and I'm not critiquing the design pictured above. It just got me thinking that it can't be good to have that pipe flexing that much. So this is a recommendation I am making for Algae Scrubbers with screens over 24" wide. But check out that growth!!! That's 6.5 pounds of algae (drained).

NOTE: I left that above section in here because I just love that picture. But the reality is that unless you are feeding about a 1/4 cup of food per day, you’ll never, ever need an Algae Scrubber this big. Read on…

Pipe Diameter

When running an Algae Scrubber fed directly from the overflow, there is usually no need to deviate from the size of the drain pipe that you currently use. But, that all depends on your total resultant flow to the pipe, length of screen, etc. In the majority of cases, this doesn’t change anything. However, if you had a large tank, and were combining four 1” drain lines together to feed one large Algae Scrubber, you have different considerations.

If you're doing a pump fed Algae Scrubber, either top of tank or sump, try to match the size of the slot pipe and other PVC components to the recommendations from the pump manufacturer, and if in doubt, err on the side of larger pipe. Larger pipe puts less head pressure on the pump, which will increase the flow rate.
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