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Unread 07/10/2008, 02:27 PM   #50
paulsilver
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Join Date: Feb 2007
Location: Portsmouth RI
Posts: 201
I too don't mind being PM'd for a thread whose topic I had previously shown interest in, but I can understand how some may... and even if the poster intends to market the scrubber as a product at some point, why does that mean it is any less interesting to me?

So, I really like the compact size of this, assuming it will work.

That said, I have the Dynamic Aquaria book here on my lap. Adey states that their research showed that: "algae, in a well developed turf, can absorb typically 0.3 to 1.2 grams of N a day per square meter of screen." He goes on to say that too much scrubbing can result in reduction of N levels to where blue Green algae dominate, which absorb less nutrients than the turf algae does. His examples indicate a scrubber size of about 3.3 sq cm per liter (120 gallon coral reef aquarium) This is well more than 1 sq. inch per gallon... more like 3 sq in per gallon. So the size might need to go up to gain the action Adey reports. And this assumes high lighting levels using MH intensity bulbs. Lesser light intensity will result in lesser algae production, and so less nutrient extraction. Important point...

He stresses the need for intense lighting on the turf scrubber... he uses metal halides in most instances... just FYI, so his analysis of nutrient removal rates depends on the high levels of light, which he also says is a goal of the surge, which creates shimmer, and intensifies the light reaching the algae.

As far as I can tell, the surge issue pertains to creating a natural surge environment in the scrubber which maximizes metabolism in the turf algae, according to the book: "Assuming adequate light, algal production is limited only by inadequate exchange of metabolites -- oxygen, carbon dioxide, and nutrients -- between the water and the cells of the attached algae. We have demonstrated a strong correlation between wave surge and improved metabolic interchange: when we occasionally stop the wave generators in our main reef tanks -- while maintaining a constant rate of circulation and level of light -- immediately there is a 50% reduction of oxygen production. The surge generated by the wave maker produces a back and forth motion within the tank, preventing the development of semi stagnant boundary layers that occur when a constant flow of liquid passes a fixed object. A steady current would tend to pin the filaments in an immobile position, and a surface layer of very slow moving water would develop." So say Adey and Loveland.

So for their model, the surge action is deemed an important aspect of the scrubber, keeping the algae moving and enabling higher rates of metabolism, which means faster growth, and better nutrient export. Refugia just don't do this as well, but they seem to work for me.

As for comparisons with refugia, I would have to say that Eric Borneman has said that he felt a refugium would have to be about the same size as the display to have a real impact on water quality, but that it is fine to be smaller if using it as a refugium for pod growth rather than as a scrubber. So I can say I agree with small being effective, so Borneman supports the size ratios described in Adey to some extent, when he talks about refugia and size. Yes, in this instance, size does matter... ;-)

Never the less, I use a Chaeto based scrubber/refugium on my 210 + 90 = 29 that is only 75 gallons in size, has a deep sand bed (6") and a few pieces of LR... it acts to reduce nitrate somewhat, and also Phosphate to a greater degree... My feeling is that the Nitrates are removed more through the deep sand bed action than by the algae scrubbing, and that a good portion of the phosphates are as well. But still I use the Chaeto. And the 75 is nearly full of it, tumbling around in there.

As for the cleaning I would be very careful with the electrical aspects, as pointed out by Dendro982 above, both in terms of splash, creep and seepage, but especially when removing and replacing the screen... perhaps there should be some accommodation for sliding the box away from the lights for the screen removal.

Regarding Spray bars: these tend to clog, almost without exception, so the holes for this, and for the drain must be large enough to make this a non-issue, and must be cleaned regularly. So I would look to this issue as well.

So, where to now?

Perhaps a larger size is needed, but since lighting can be done from both sides, the box/screen combo might need be only half as large as a more traditional scrubber. But still much larger than discussed so far, as per both Adey & Loveland, and Borneman. At least according to these experts. Technical issues such as the cleaning and spillage/creep are in need of addressing, especially for a "commercial" version.

Hope this helped, and hope to see more comments here.


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