Algae Scrubber Basics
- Thread starter srusso
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Question on algae scrubbers. I seen that they either hang above the surface of the water (waterfall type), or are submersed but have an air pump incorporated into the design (up flow type). In both cases the screens are exposed to air. Is air a necessary component or, in the case of the up flow, just used for water flow?
Do I NEED a source of air in the design of the algae scrubber?
Do I NEED a source of air in the design of the algae scrubber?
Floyd R Turbo
Either busy or sleeping
For a UAS, yes. For a waterfall, no. Meaning you don't need air infused into the water flow.
SantaMonica
Well-known member
Air is always needed to create an a turbulent air/water interface; this gets carbon from the CO2 in the air to the algae the fastest. On a waterfall, the air is about 3 mm away, and on an upflow it's about zero.
Floyd R Turbo
Either busy or sleeping
Rant warning.
Here we go again with the water-air-water thing caused by a bubble passing through algae. Sorry, IMHO this is the exception to the rule.
An algae strand moves out of the way of a passing air bubble. It doesn't pierce it allowing the algae to get exposed to the air inside the bubble. The bubble's surface tension would not allow this. Or should I say, I do not believe the bubble's surface tension would allow this. That makes my statement more opinion that fact, as I can't unequivocally state that this is indeed a fact all of the time.
IMHO. It makes much more sense logically that the reason that a UAS grows algae much faster than the same algae in another area of the same system (rock, substrate, etc) is due to the random action of the water itself as the bubble passes through it and that algae that is submersed in it. This is related to creating high levels of motion at the boundary layer, which is where the nutrient exchange happens. This is also where the gas exchange happens. On a microscopic level.
The boundary layer is broken down in a UAS by way of the water motion created by the bubble passing through a submersed mat of algae.
The boundary layer is broken down in a waterfall scrubber by way of a thin laminar sheet of water passing at free-fall speed through the algae.
CO2 and O2 are dissolved in the water and exchanged at the boundary layer. Bubbles passing through water are (probably) more likely to cause the air in the bubble to dissolve into the water than they are to let a strand of algae into it's interior. Direct exposure to open air is actually more likely to happen from a free-hanging vertical waterfall scrubber as the algae grows thicker than it is to get it from a passing bubble.
Try to split a bubble in two with a razor blade. The majority of the time, the bubble moves around the razor blade. The only time it splits it is when the bubble lines up top dead center with the sharp edge of the blade, and then the bubble splits into 2. Of course, this depends on the bubble size so let's say it's the size generated by a UAS or airstone - let's say pea size. So you're saying that a strand of algae is just as likely as a razor blade to rip through the surface tension of a bubble. Ok.
Told you it was a rant. I'm tired of that theory.
Floyd R Turbo
Either busy or sleeping
I should also state that I don't believe that algae on s waterfall scrubber exposed to air is likely to have a great effect on gas exchange. This is likely to still primarily happen at the boundary layer as water passes
Mark...
Member
Thought I would post a couple pics of my third harvest. Last one was 14 days ago.
Note, 2 different shades of green. (no not gray)
Serious growth, may I ask what light you are using?
hkgar
Active member
I am using two 60 watt CFL's rated at 2700k. I started this cycle with two of these LED lights
http://www.amazon.com/gp/product/B00MXTWP9U?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
but wasn't happy because the blue created a "hot spot" right in the center and I got no growth there. I only used them for about 3 or 4 days.
http://www.amazon.com/gp/product/B00MXTWP9U?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
but wasn't happy because the blue created a "hot spot" right in the center and I got no growth there. I only used them for about 3 or 4 days.
Floyd R Turbo
Either busy or sleeping
Usually those lights come with a bezel that you can remove and take the lenses out. That one doesn't look like it does. Also they are all pretty tight together, so it's not just the blue that was the issue I'm guessing. There is a sweet spot for those type of LED lamp, backing it off 2" or so might have solved the issue.
hkgar
Active member
Actually I was just thinking, as I wrote the last post, that I might have had them too close. At the distance I had them, they formed a spot light in the middle of the screen and didn't light the whole screen.
I think I will try using one again and moving it out to provide better coverage. Then maybe monitor one side versus the other.
I think I will try using one again and moving it out to provide better coverage. Then maybe monitor one side versus the other.
Floyd R Turbo
Either busy or sleeping
normally you would also direct these perpendicular to the screen. However if intensity is a problem, you can try positioning them slightly higher, and point them down. This might stretch the hotspot out a bit as well. Note that I haven't tried this, but it makes sense....
SantaMonica
Well-known member
If you look at a waterfall, the water is about 3 mm deep. If you look at an upflow in slow motion, the bubbles hit the algae directly.
Floyd R Turbo
Either busy or sleeping
I refer back to my prior post about this
jason2459
Well-known member
I can't tell the thickness by looking at it. But something still doesn't make since here to me but I'm genuinely curious. Don't aquatic plants absorb oxygen from what's dissolved in the water(DO)? Which if I'm not mistaken in our setup is mainly caused by turbulent water which looks like to me is established effectively by both types of systems if maintained properly. Just the turbulence is created by bubbles in one and the other through water flow. I don't see the bubble itself being necessary or where the algae gets its oxygen from directly. At least not with aquatic plants.
mattberrytr
New member
Yep. SM keeps harping on about this because it promotes his upflow algae scrubbers, which use air bubbles. He's pretty much stating that there is more CO2 available to the algae with an upflow scrubber, and therefore implying they work better than waterfall scrubbers.
herring_fish
Crazy Designer
I have to agree.
Look at the old posts. …the 6350’s. This has been covered …ad nusium.
We are not talking about the underside of a tree leaf. Algae is adapted to absorb CO2 most efficiently via direct water to cell contact, not through air to cell contact. In nature, algal growth is strongest at the water line that stays submerged throughout the tidal cycle, not at the line that is out of the water part of the day or with intermittent splashing. This is also born out in the lab. Do we need to belabor this?
The advantage of air injection hopefully creates turbulence. Turbulence of most any kind brakes down boundary layers/matting but bubbling does not improve respiration directly. If anything, air cuts down on the time that water is in contact with the algae cell walls (contact time). In sales, you are taught that when you have a problem, you turn it into a feature.
On another note: In reading back, I realized that there was a point that may have been overlooked.
“….algae only absorbs a small percentage of nutrients per pass, similar to eating at a buffet: you can only eat so much; having more food there will not allow you to eat more….”
I have to disagree here. Scrubbers work better with higher nutrient levels, not lower. Football players gain more wait at the college cafeteria than at Jenny Craig’s restaurant. You also send them back for more passes, that part is true. Of course this is self-evident, isn’t it?
It seems to me that creating a high differential is not a good idea if that is the only reason for doing it. There may be other great reasons for recirculating water inside a scrubber but not long term growth output.
If there are high nutrient levels during any given pass, algae will grow better. Recirculating water inside of a scrubber will lower the available nutrients or food and therefore growth will slow. You want more water from the higher nutrient areas of the system not the lowest.
With that in mind multiple passes of water from the highest nutrient areas is best. More total intake means more growth. More growth offers more total export. More total export means better total nutrient control in the total system.
That usually means taking it from the display tank. Yes?
Look at the old posts. …the 6350’s. This has been covered …ad nusium.
We are not talking about the underside of a tree leaf. Algae is adapted to absorb CO2 most efficiently via direct water to cell contact, not through air to cell contact. In nature, algal growth is strongest at the water line that stays submerged throughout the tidal cycle, not at the line that is out of the water part of the day or with intermittent splashing. This is also born out in the lab. Do we need to belabor this?
The advantage of air injection hopefully creates turbulence. Turbulence of most any kind brakes down boundary layers/matting but bubbling does not improve respiration directly. If anything, air cuts down on the time that water is in contact with the algae cell walls (contact time). In sales, you are taught that when you have a problem, you turn it into a feature.
On another note: In reading back, I realized that there was a point that may have been overlooked.
“….algae only absorbs a small percentage of nutrients per pass, similar to eating at a buffet: you can only eat so much; having more food there will not allow you to eat more….”
I have to disagree here. Scrubbers work better with higher nutrient levels, not lower. Football players gain more wait at the college cafeteria than at Jenny Craig’s restaurant. You also send them back for more passes, that part is true. Of course this is self-evident, isn’t it?
It seems to me that creating a high differential is not a good idea if that is the only reason for doing it. There may be other great reasons for recirculating water inside a scrubber but not long term growth output.
If there are high nutrient levels during any given pass, algae will grow better. Recirculating water inside of a scrubber will lower the available nutrients or food and therefore growth will slow. You want more water from the higher nutrient areas of the system not the lowest.
With that in mind multiple passes of water from the highest nutrient areas is best. More total intake means more growth. More growth offers more total export. More total export means better total nutrient control in the total system.
That usually means taking it from the display tank. Yes?
Last edited:
jason2459
Well-known member
Ok thanks, so I'm not totally crazy.
As for where the highest nutrient levels are in our tank I can't believe it would make any difference between sump and display as again I would think its the dissolved solids they are consuming which in our small systems would be pretty much equal everywhere in the water column. Unless you tap into something under the sandbed like an under gravel filter. Which I happen to run a reversed flow one in my sump. So, now I'm wondering if an algae scrubber that can pull from the outflow of an under gravel filter would be the most efficient. I have my water fall pump sitting right on top of the dolomite of my RUGF.
Multiple passes would occur regardless in our small eco system based on gph of circulation.
As for where the highest nutrient levels are in our tank I can't believe it would make any difference between sump and display as again I would think its the dissolved solids they are consuming which in our small systems would be pretty much equal everywhere in the water column. Unless you tap into something under the sandbed like an under gravel filter. Which I happen to run a reversed flow one in my sump. So, now I'm wondering if an algae scrubber that can pull from the outflow of an under gravel filter would be the most efficient. I have my water fall pump sitting right on top of the dolomite of my RUGF.
Multiple passes would occur regardless in our small eco system based on gph of circulation.
herring_fish
Crazy Designer
I agree. I was talking about an "œNth degree" situation. There is very little differential between one area and any other open parts of a typical system. Drawing it from anywhere that is exposed to the direct circulation of the pumps is going to yield virtually the same results.
As for the RUGF, the change in nutrient load may be very hard to predict. If it is at all measurable at any given point it would probably be small and may not be worth your effort. Most people draw their water from the sump. I only mentioned the display to represent the main body of water, particularly because I don't have a sump in line with my main circulation and that is only because I have been a lousy plumber in the past.
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