What led me to start this thread was this paragraph on the SURF2 thread http://algaescrubber.net/forums/show...2243#post32243
There are a few interesting points to discuss in this above paragraph. Let us start with this one:
I don't know if anyone else caught this, but this basically acknowledges what I have been saying for a while - the Upflow type scrubbers have inherently low-flow, because the action of bubbles rising does not pull water through the unit at a significant rate. Admittedly, the UAS flow rate is nearly impossible to measure, but I think this is something that we can all agree on, specifically, when compared to waterfall scrubbers.
The "dwell time" concept is not really new, but the SURF seems to make it a priority. I would agree that the water exiting the unit should be very low in nutrients when compared to the rest of the tank water. However this is not a concept or technique that is necessarily limited to the SURF or UAS type scrubbers - not at all. It's not even limited to scrubbers. All one would need to do in order to create a similar low-nutrient ecosystem with any other scrubber (waterfall, dump bucket, you name it, any scrubber) or any other filtration system in general is to put the supply (pump) in the same compartment as the effluent (outflow) and then regulate the rate of influx of "dirty" tank water.
There is a give and take with the dwell time issue:
UASs (HOG, SURF, etc) = Smaller amounts of water that is a lot cleaner than the rest of the tank water
Waterfalls, Horizontals = Larger amounts of water that is just a bit cleaner than the rest of the tank water
One could recirculate the water from one end of their sump to the other and pass all the water through the entire filtration system repeatedly, and then have a low flow/return from the tank and achieve the same thing. But does this necessarily mean that such a method is more effective at filtration? I would say at best, it is just different - 6 of one, half dozen of the other. Each has their pros and cons, that's all.
Now to the middle sentence:
The reference to greener growth occurring sooner in a low nutrient environment does seem to be true in many cases. When you put a waterfall scrubber on a tank that is in really bad shape, it takes a while to go through the dark growth stages. The point at which the algae really turns green and takes off, to me, is not really established. It's too hard to put a finger on exactly what causes a screen to go green fast. I have had customers put one of my units on their tank and literally get a solid mat of thick emerald green in 10 days. I have had others take months to get anywhere close to green.
I think it's safe to say that GHA is better at filtering when compared to other forms of algae that might grow in high nutrient water (like brown slime, black slime, yellow, etc). Dr. Adey's research has always claimed that true Turf Algae has a higher rate of uptake (fixation), and (I assume) that's why he chose to build his Algal Turf Scrubber the way he did (admission: I still haven't read Dynamic Aquaria...). The advent of the waterfall scrubber has really amped up the ability to grow GHA faster due to the slot pipe, proximity of light, rate of flow, and uses of more efficient light sources. So it may not actually be that GHA is better at filtering, but rather that our method of cultivation (growth) is just that much more effective. Again, none of this as actually been (recently) studied scientifically and specifically related to how we in the scrubber community implement these methods. Well there was a tangent...back to the point now!
I think the true test of this idea would be to put a scrubber on a high nutrient tank (any scrubber) and let it grow in a restricted volume environment. In a way, I had planned on doing something like this with my grand experiment plan, which will probably never happen because I don't have the time. But anyone could take their scrubber and make this happen - except those that feed their waterfall scrubber directly from their overflow (must be a pump-fed scrubber)
Next up:
I'm still not sold on bubbles being the key. My UAS test unit has a bubble bar that clogs up in just a few days, and this forces all the air to come out of a few of the holes. I get just as much growth on the areas of the screen that has zero bubbles "rubbing" on them as I get in areas where all the bubbles go. Even the SURF has GG on the bottom/sides of the box, which are well and far away from direct bubble contact, yet these surfaces grow algae also.
When I clean out my UAS, I get just as much growth on the submerged acrylic surfaces as I scrape off the screen. I can scrape the screen, put that in a pile, then scrape out the box, and put that in another pile, and they are about equal. All of this algae is very loosely attached - running the screen under tap water release most of it without even touching it. After over a year of growth, I can wipe the screen clean of growth with my fingertips, leaving a screen that is just stained green, with no growth stuck in the holes.
This is in contrast to my waterfall scrubbers - using the same light and proximity - which need to be scraped, and the algae gets more strongly attached with each cleaning, and the screen holes get filled in with algae that needs to be scrubbed with a stiff brush to be removed (which I don't do).
In my experience, algae adapts to it's environment. If you put it in an environment without a lot of high-speed laminar flow, such as UAS, it will not need to anchor strongly. If you put it in an environment with high speed laminar flow, such as a waterfall or even some horizontal scrubbers, it will anchor strongly.
I do agree that rough surfaces, in general, are critical for algae attachment. However, this is more of a long-term issue with UAS based scrubbers. I think the more correct statement is that extremely rough surfaces, like the GG surfaces, are much more critical for UAS type scrubbers, as the algae just doesn't need to attach strongly. The GG surfaces essentially force the algae to attach more strongly.
What I'm saying is that the plastic canvas is the wrong material for the UAS type scrubbers. We didn't really know it, but it always has been the wrong material, and it likely has been the reason why so many people have had problems with UAS scrubbers not performing well. I think the GG surface is a great thing for the UAS scrubbers, but I really wish, Santa Monica, that you would stop slamming on waterfall scrubbers and plastic canvas.
References have been made (by Santa Monica) about the plastic canvas having a wax coating for releasing it from the injection mold, and even one post that suggested that the screen was coated in PTFE (Teflon), neither of which is true. I spoke with the manufacturer, and examined screens before and after boiling/rinsing/scrubbing/bleaching, and there was no difference. For some reason, rather that promote the advantages of the GG surfaces for UAS applications, you decided to wage some sort of campaign against plastic canvas in general.
Plastic canvas is, IMO, an epic failure for use in the UAS. I feel pretty comfortable saying that. I can respect that you don't want to divulge the GG material. It does seem like the perfect material for the UAS scrubbers, which you have applied for the patent on, and worked very hard to develop. I can also understand why you might be reluctant to admit that the plastic canvas was the wrong material (in general) for UAS type applications (even though it does work well for some, just not consistently).
The plastic canvas is still the perfect material for the waterfall scrubber. Algae can attach to it quickly, if it is properly roughed up, and if the rest of the scrubber is properly built. Speed of attachment and growth depends on many factors, not just the screen material. Algae will anchor to plastic canvas strongly over time, and will fill in the holes, which allows for rapid re-growth. I have never had detachment issues on any of the scrubbers I maintain - even with super-thick 3D growth. The material is very durable, easy to scrape clean, and as long is it is initially roughed up properly, it should really never need to be replaced, unless it gets torn from scraping too hard - I have yet to tear a screen.
Necessity is the mother of invention. If the Plastic Canvas worked as well as it does in the waterfall scrubbers, you may not have had the need for coming up with the GG material. If your tank had not cracked and forced you to put everything into a tub, you may never have come up with the SURF.
...I had to cut this short and attend to business, still have a few more comments to add, eventually...