Algae Scrubber Build Basics, Summary Post 1 of 2
Algae Scrubber Build Basics, Summary Post 1 of 2
Algae Scrubber Build Basics, Summary Post 1 of 2
This thread has really taken off, and I'm happy to see so many people interesting in building algae scrubbers. Just so everyone doesn't have to read through this entire thread to understand the concept and get most of their questions answered, I will try to summarize.
There are many options when it comes to building your own scrubber. Hopefully this post 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.
In the future, I will prepare another summary which should cover problems with your scrubbers, and how to pinpoint the issue. However, 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 a scrubber, but there is always a cheap and easy way, as well as the most effective and efficient way.
I make several references within this post to the Algae Scrubber site. Reef Central generally blocks links to other forum sites. So you might have to search a bit for a thread I reference, but I'll do my best to get you pointed in the right direction. The site is algae scrubber dot net.
Slot Tube and Screen Material
The principle behind the vertical waterfall style algae scrubber is that you can light it from both sides and place the lights very close, which requires less light and material than the older horizontal style, and vastly increases growth. 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 by zip ties running through a cut-out section of the screen.
from my scrubber
Others have come up with other ways of doing it also, like by using shower curtain rings (plastic ones - see pics of Amphiprion's build under the "Protection" section) or sections of PVC pipe, one size larger that the slot tube
pic of waucedah_joe's scrubber on the Algae Scrubber site
Most use zip ties. They work the best, they're cheap at Wal-Mart, so you just replace them with each cleaning. Or you can do like I do, and pry the locking part open with the tip of a razor blade, and re-use them until they are worn out, which seems to be around 2 or 3 months. Or, you can find releasable zip ties, but you have to buy them 50 at a time (or at least, that's all I've been able to find)
Planning your Scrubber
From post #1
The very first step you need to do before buying, measuring, or sketching up anything, is to decide how you are going to supply your scrubber, and determine what your available flow rate is. For a top-of tank design (not shown in the picture above), you would need a separate riser pump to feed the slot tube. For a sump design, there are 2 ways of doing it. Fed from the drain supplying the sump, or fed from a separate pump. The former is what people usually do.
In any case, you need to measure the flow rate. Do this step. It is critical. Do not, I repeat,
do not calculate the flow rate based on pump curves and head-feet of pressure. This may sound like a total pain in the behind, but just trust me on this one. Would you rather go through all the effort of building a scrubber, only to have problems and find out that you didn't have as much flow as you thought you did? Believe me, I've been there.
If you've been reading this thread, you will see that at some point I started making a big deal about this. The reason is that it is a big deal and I think many people don't realize that their pump does not pump at the rated flow, and in the majority of cases, it doesn't come close to the flow calculated by using a standard head-foot calculator program or table. Not even close. So I have chosen to make it the #1 priority for scrubber design, hands down.
You have to know your actual flow.
For a drain fed scrubber, fill a pitcher with the water entering the sump. You will probably need to rig up a temporary pipe or routing configuration so that you can fill the container. For a pump-fed scrubber, set up the pump in a sink filled with water to the same level as your pump will be submerged, and connect the tubing required to reach the height of the connection to the horizontal slot tube, so that you mimic as best as possible the actual conditions.
Now that you've done all this, fill the container and record the time it takes to fill it. Do this at least a dozen times. The way I do this is by using a recording device, like a digital voice recorder or a cell phone and just calling out "Go" and "Stop", then afterward, playing it back and using a stopwatch to get the time intervals. You could also have someone else run the stopwatch and write down the times. Average out the times and then figure out how many gallons per hour of flow you are actually getting. If you have multiple drains, measure and extrapolate GPH for each individually, and then add together.
For instance, if you are using a 1/2 gallon pitcher, and it takes 4.5 seconds to fill it, then you would have (0.5 gallons / 4.5 seconds) x (3600 seconds / 1 hour) which would be 400 GPH.
Don't be surprised if you have a lot less flow from your pump than you thought you had. I had less than 1/2 of what I thought it was. Head-feet calculations are usually way off, because most people don't use big enough return hose or have other restrictions in the plumbing. Some of it is inherent to reef-ready aquarium design (1" drain, 3/4" return, Danner Mag-Drive 9.5 and larger pumps need 1.5" return, see a problem?). So don't feel bad. A lot of people are in your situation, but they just don't know it. Really.
Start with a clean pump. If your pump is not clean, soak it in vinegar for 15 minutes and scrub it good. After running a scrubber for about 4-5 months, your pump flow will drop about 15%, and by 6 months, it will have dropped by
25%, so you want to know your best-case flow and build around that. It's a lot easier to start with a throttled-back clean pump and open it a little when the flow rate decreases. Figure out your system flow rate, multiply by 80%, and that will be a good starting point. But, it's not going to kill you to start at full flow, and end up with a little less over time. You might just want to clean your pump a little more often, say every 3 months. So it's up to you. Just being aware of your system conditions puts you miles ahead.
Screen Size
Once you figure out your flow point, then it's time to figure out your optimal screen dimensions.
There are 2 ways of looking at this: square inches based on length and width
dimension, and square inches based on
illuminated surface area. The latter is technically more accurate, but since most people light both sides, the
former is usually referenced.
For every gallon of water in your display tank, you need 2
total square inches of illuminated screen material. This means that if you run a screen that is vertical and lit from both sides, then you need a screen with dimensions (length times width) that is equal to the size of your tank, or
1 square inch of material per gallon. This is what you will see commonly referenced, and what I continue to reference for simplicity's sake. Double the dimensional measurement for a vertical screen, lit from only one side. Double it again for a horizontal or slanted screen.
Sizing of the screen does not require inclusion of the volume of water in the sump. Note that this is a correction from most of what has been posted previously (even by me - oops).
So, just so we're 100% clear on this:
Vertical, lit from both sides:
1 square inch of screen material per gallon (
2 square inches of illuminated screen area per gallon)
Vertical, lit from only one side:
2 square inches of screen material per gallon (which is
also 2 square inches of illuminated screen area per gallon)
Horizontal:
4 square inches of screen material per gallon (
4 square inches of illuminated screen material per gallon). Lighting must increase also (noted below). Also note that
this is a correction to what was listed on Post #1 of this thread (that post listed that a 10 x 10 screen was good for 40 gallons, instead of 25 gallons)
Screen Dimensions
So now that you know your actual flow rate AND the total size of your screen (and you need to know the total dimensional area for this part, not the total surface area), now you are ready to figure out your dimensions.
You want
35 GPH per inch of screen width. Simply take your GPH (that you just measured) and divide by 35, and this will be your optimal screen width. Then, take that number and divide it into the gallon size of your display tank to obtain the height dimension of the screen. Use the
size of your tank, not the gallons that you think are actually in it (so do not account for volume of Live Rock, fish, decor, etc) and do not include your sump volume. The result is the total area of roughed-up screen that you want.
In general, you want to add at least one inch to the height dimension for the section of smooth screen that will be inserted into the slot tube. Specifically, you want to allow for the distance that the screen will be inserted into the slot, plus at least 1/4" of smooth screen below the slot tube to help prevent algae growth into the slot, so this "one inch" is just a good rule of thumb, and should be increased depending on the diameter of your slot tube. A little extra smooth screen at the top never hurts.
The critical area, and the only area that contributes to scrubbing power,
is the roughed-up and illuminated portion of the screen.
Pipe
As far as pipe diameter is concerned, just match the size of the drain pipe that you currently use. If you're doing a pump fed scrubber, either top of tank or sump, try to match the feed tubing and components to the recommendations from the pump manufacturer.
The slot tube 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. This is especially true for a large 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.
pic of yesman's scrubber (from the algae scrubber site)
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 new recommendation I am making for scrubbers with screens over 24" wide. But check out that growth!!! That's
6.5 pounds of algae (drained).
Cutting the Slot
This arguably the most difficult part of building a scrubber.
The width of the slot should be approximately 1/8" wide, the same length as the screen which you are using (as exact as possible), and as straight as possible. The best way to cut the slot straight is by using a table saw, and being very careful. Since most people don't have access to a table saw (or aren't very careful), a dremel with a cutoff wheel it the most popular way of cutting the slot. This takes time and patience. Mark the slot, and cut carefully.
If you mess up, do it again. PVC pipe is cheap. Once you solvent weld it and endcap and a union to it, it is not as cheap to replace (but still relatively cheap)
From the Algae Scrubber site (also posted in this thread)
Screening Material
The search for the "perfect material" for growing algae in the vertical waterfall configuration has always come back to the same material, the
#7 Mesh Plastic Canvas, roughed up with a
hole saw or a rasp. You can feel free to experiment, but this material has been proven to work over and over again.
A new screen is slick and smooth. It needs to be roughed up so that the algae has anchoring points. Once the screen is established, algae can grow very thick, and it will get heavy. I have seen pictures of screens that weigh several pounds. This weight is distributed across the screen, and with a rough base, it will hold very well.
from the Algae Scrubber site
The top section of the screen, where it is inserted into the slot tube, should not be roughed up at all. This helps prevent algae from growing into the slot and blocking the flow. This is really not of major concern if you properly cut the slot, so no additional steps should be necessary. The reason is that if algae happens to grow up into the slot tube, the water pressure will increase, which will inhibit the growth of algae creeping further into the slot. A balance point is achieved.
Slot Tube Crosscuts, and others
Originally, it was recommended to place crosscuts in the slot tube. You will see this on older builds.
This is not recommended anymore, so don't do it. The idea was to allow for water to continue to flow if the algae grew up into the slot and clogged it, and also to prevent squirting. The result was that algae grew easily into the slot, because the pressure wasn't high enough to prevent it - flow was just diverted to the crosscuts. Then, the pressure was higher through the crosscuts, which resulted in squirting. The solution is the perfectly straight and correct width slot.
There have been many other attempts to 'improve' on the slotted tube design, but for one reason or another, they just don't work as well. I could list and describe them, but many of them are pictured on the Algae Scrubber site, under the sticky topic "Hundreds of new design pics are posted...".
Continued, see next post (unless someone sneaks in a message)
