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Thread: cyano scrubber? ...and also, mud

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    cyano scrubber? ...and also, mud

    Hi, everyone. Long time no see.

    I've had phosphorous on my mind for a while, now, and I've come up with a notion or two that might be of interest in these parts. As before, apologies if what I'm pondering has already been pondered, but I do like to geek on this stuff...

    I strongly believe the LED gurus are on to something with their recognition of the need to provide a broader spectrum to facilitate bacterial photosynthesis. More on this later, but first, here's my take on the P problem...

    I suspect the root of the problem is that we're trying to pull P out of our systems using organisms that are "P-lite" -- that is, the N:P ratio in the algal cells is higher than the Redfield ratio of 16:1 (...which, it should be recalled, is the average N:P ratio of all the stuff scooped up by plankton nets and is most likely not the N:P ratio that would be found by sampling any particular species, or any particular cell, of bacteria or algae). This makes sense in that cyano dominates at low N:P ratios (like 10:1 and below) while green algae outcompetes cyano for P at high N:P ratios (above 20:1). In other words, the problem is the scrubber itself in that it creates an environment so favorable to green algae that it can outcompete cyano even under conditions (low N:P ratio) that should strongly favor cyano. But even so, it's still just green algae, so it simply can't absorb P fast enough to keep up with what's going into the system.

    Put simply, if the food going into a system is around 16:1 N:P, then algae with an internal N:P ratio of 18:1 or 20:1 or even higher (see Redfield Ratio is not always 16:1 in phytoplankton) can't possibly keep up. It N-limits itself.

    The obvious solution here is to dose N, like the FW guys who practice estimative index dosing, but I would argue that dosing macronutrients in a reef tank is inherently risky. To err is human, after all. Besides, from what I've read around here, that doesn't seem to work... My guess is that the problem isn't a micronutrient deficiency; rather, the problem is that not just the algae but the entire microbial loop is starved for nitrogen, and because bacteria are much, much better than algae at capturing nutrients during times of surplus and storing them for future use, that's where most of the N ends up.

    So like I said, seems to me the LED guys are on to something with the idea of including bacteria-friendly wavelengths -- if you can't beat 'em, join 'em... I'm thinking, though, that maybe we, as algae-friendly folk, should be looking beyond the display tank to consider the lighting needs of cyanobacteria.

    I'm thinking that perhaps what's called for here is a cyano scrubber. Cyano totally hearts low N:P ratios to begin with, so why fight it? The tinkerers and LED guys out there (Floyd, I'm looking in your direction...) may want to consider two-stage scrubbers, with a "normal" scrubber emptying into a low-flow area (maybe even just a sump) that's lit to foster the growth of cyano after N zeros out, or perhaps building scrubbers that can be transitioned from high flow and lighting for green algae to low flow and lighting that's optimized for cyano.

    But until somebody figures out whether or not we're all going to have to become cyano farmers, too, as a stopgap solution for P accumulation, I've been considering plumbing a "remote deep mud bed" in a five-gallon plastic bucket into my system. I've been running an algae scrubber since Day 1 and because my DT is small, I don't feed heavily lest my corals outgrow their happy home, so my P levels are still quite low, but "low" isn't undetectable... I can see the writing on the wall at this point.

    The reason I've got mud on my mind is that in an anaerobic environment, chemical conditions change such that bacteria can reduce P compounds to orthophosphate (PO4) which persists in the absence of oxygen and, being readily soluble, accumulates to concentrations far higher than what's detectable in the overlying water. Orthophosphate likes to adhere directly to mineral surfaces, so the optimal nutrient sink for P should combine anaerobic reducing conditions with a lot of available surface area per unit volume -- ie, a small grain size, like fine sand or mud... So it's no surprise that "Miracle Mud" and similar products are out there -- not only are they better simulations of the seafloor than pool filter sand, but they're excellent nutrient sinks, as well.

    But I'm looking for an inexpensive alternative -- has anyone ever tested river clay from the local art store for P loading? -- because my idea is to let the new mud bed cycle and come into equilibrium with the rest of the system, and then dump it, along with any benthic organisms that managed to colonize it (...just more nutrients to export!), and start over with fresh material. Obviously, I'll never zero out P this way, but P should migrate -- very slowly, over the course of months -- from the established substrate into the RDMB; that is, phosphorous will gradually diffuse out of the area of high concentration and into the area of low concentration. I'm not really worried about P accumulation in my substrate yet, but if you are, this might be worth trying, as it's simple, comparatively cheap, and very low maintenance.

    The basic idea is that much like a scrubber establishes a "sweet spot" in the system where the environment is optimal for the growth of green algae, a remote deep mud bed would be a sweet spot where phosphorous will want to accumulate. And like an algae scrubber, it has to be cleaned regularly to be effective... Happily, "regularly" in this context probably means something on the order of once or twice a year. Like I said: low maintenance.

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    cyano dominates at low N:P ratios (like 10:1 and below) while green algae outcompetes cyano for P at high N:P ratios (above 20:1)
    Where do you find this research?

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    This is old hat. It predates the interwebs, so it turns up in textbooks and is pretty much taken for granted -- like the ocean's food web being dominated by bacteria, not algae.

    The 10:1 and 20:1 ratios absolutely should not be taken as gospel, BTW; it's more like 10:1 and 22:1. I just put up ballpark figures from memory meant to emphasize that as the system's nutrient balance drifts away from 16:1, conditions will inevitably come to favor either cyano or green algae (...or diatoms if Si levels are high).

    And be sure to follow the link at the bottom of Mr. Algae's page.

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    I know about bacteria; I meant the ratios.

    I'm sure the Chuck fellow means well, with the two tanks they tested, and the "it seems to indicate", but I was more referring to actual research on the ratios and biology such as found in journals that do thousands of tests...

    Reefbase.org
    Int-res.com/site-service/search
    data.aims.gov.au
    plankt.oxfordjournals.org/content/by/year
    tos.org/oceanography/issues/archive.html
    terrapub.co.jp
    aslo.org/lo/search.html
    bioone.org/search/advanced
    www.aoml.noaa.gov/general/lib/CREWS/
    bioone.org/loi/jnbs
    jstor.org/action/showPublication?journalCode=jnortamerbentsoc
    springerlink.com/content/100407
    springerlink.com/content/100441
    onlinelibrary.wiley.com/journal/10.1111/(ISSN)1529-8817/issues

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    First off, SM, I must respectfully note that you're declining to address my actual thesis, which is that green algae with an N:P ratio higher than the N:P of the food going into an aquarium cannot possibly remove all the P without supplemental nitrogen. This seems intuitively obvious, and it troubles me. Is the N:P ratio of the algae in the scrubber known to be lower than 16:1? Aren't bacteria typically P-heavy and algae P-lite, relative to the Redfield ratio? Can you establish that I have erred by presuming that scrubber algae is, like most algaes other than cyano, P-lite? Failure is the road to wisdom, sir, so I beg you to please explain my mistakes and perhaps even join me as I ponder and seek to correct them.

    But if you want real science and hard numbers, I respect that. Here you go.

    Here's a cut'n'paste of the salient bit:

    --

    The nitrogen : Phosphorus ratio as a factor regulating phytoplankton community structure : Nutrient ratios
    (by: BULGAKOV N. G. and LEVICH A. P. ; Moscow State University 1999.)

    ABSTRACT: Shifts in phytoplankton species composition following changes in N: P ratio have been observed in artificial laboratory microcosms and natural phytoplankton communities in vitro and in situ. The experiments reported and reviewed here have shown that high N: P weight ratios (20-50: 1) can favor the development of Chlorococcales, while a reduction of the N: P ratio to values of 5 to 10 frequently leads to a community dominated by Cyanophyta. Model calculations predict that the relative abundance of different phytoplankton species depends only on the relative amounts of N and P in the environment, so that the optimal N: P ratio for a given species is equal to the ratio of its minimum cell requirements for these elements. An empirical test of this hypothesis showed that for several species of Chlorococcales and Cyanophyta the ratios of their cellular requirements for N and P determined experimentally were close to their optimal (for growth) environmental concentration ratios. For instance, an experimental increase in the N: P ratio from a value of 4:1 to 25-50: 1 by mass in the water of fish-breeding ponds led to an increased abundance of Chlorococcales. The species shift was due mainly to Scenedesmus quadricauda, which has a high optimal N: P ratio for growth.

    --

    Emphasis is mine, not the original author's. Like I said, this is old hat.

    I've learned to avoid citing references like that in online forums, as most hobbyists want "real world" examples of how things work in other people's aquariums -- Mr. Algae carries more weight than Dr. Levich, I'm afraid. Changing minds requires citing respected hobbyists, not respected scientists, but like you, I take science as my starting point.


    Quote Originally Posted by SantaMonica
    I'm sure the Chuck fellow means well, with the two tanks they tested, and the "it seems to indicate"
    Mockery is an invitation to others to laugh along with you in order to validate the position you've taken, and seeking validation telegraphs weakness, not strength. More saliently, if it is your wish to maintain a civil and evidence-based discourse, I suggest you lead by example. Marshall your thoughts, state your case, and provide functioning links that lead to specific documents that either support your position or erode mine.

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    34cygni - have you read this stuff. Seems like we agree on the function of dominance at least.
    http://algaescrubber.net/forums/show...ll=1#post24767

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    If you've been puzzling over cyano's relationship to P accumulation in the substrate, Garf, you may find this interesting. Be sure to mouse around over the text -- there are several links in there, but they don't show up as blue underlined text for all users. Something peculiar to the board, I believe.

    As for this...

    Quote Originally Posted by Garf
    This may not only apply to this topic but others where nutrient skewed effects are noticed. The algae requiring LOWEST nutrients become dominant. Therefore algae doing the LEAST filtering become dominant.
    There are other variables in play than simply nutrients, but yes, I broadly agree. As Dr. Levich noted, algae with an internal nutrient ratio close to the N:P ratio in the water will do best -- not the "least filtering" algae, but I think that's what you meant by "LOWEST nutrients": the algae that had the fewest leftovers.

    However, selection pressures in a scrubber are unique and they seem to be strong enough to maintain a population of green algae even when N is very low and the N:P ratio should strongly favor cyano. I wonder if the biggest variable in the selection process is actually the weekly cleaning, as it's well known that the activities of grazing animals have a profound impact on the composition of a local algae population. Basically, the stuff that the grazers don't eat takes over.

    Cleaning a scrubber screen is some pretty hardcore grazing, if you will... The algae that sticks up won't get hammered down, but it will get scraped off. But on the other hand, it only happens once a week. Weird selection pressure. I don't know what that might do beyond select for algae that grabs onto the plastic really well.

    My best guess is that it's a combination of that, the lighting, and the very high flow conditions in a scrubber that keep the scrubber algae competitive. In particular, the high flow both within a reef tank and through the scrubber turns over the entire water column through the scrubber quickly enough to give the scrubber algae first crack at the good stuff. That, at any rate, seems to me like the only way it could manage to outcompete cyano even after N zeroes out.


    Quote Originally Posted by Garf
    I will probably take a bit of beating over this but if this theory is correct then nitrate limited screens probably started out as high ratio screens which then became PHOSPHATE limited. This starved out the normal ratio algae and low nitrate : phos ratio algae took over the screen. This new algae could use more nitrate than phos, leading into a skewing of the filtration balance leaving more phos in the water column. This low ratio algae could also assimilate ammonia faster to supplement the nitrate limitation that it has caused. Hence the rise in phos..
    There may be a period when a scrubber is first attached to a mature system and you're getting lush, thick, dark growth, that a P-heavy algae is growing, but I suspect N limitation is the inevitable result of a scrubber based on green algae, and the system never becomes P-limited. The water may be depleted of P at times as heavy algae growth sucks in nutrients, but my thinking is that the scrubber will eventually zero out N, and the system will begin to accumulate P again.
    Last edited by 34cygni; 09-13-2012 at 07:51 PM. Reason: to add more info

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    Good read in that link. That's exactly the impression that I have been given after reading all the scientific stuff I could find on the subject. I find it amusing that he was totally ignored and people just carried on dumping stuff in their tanks.

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    34cygni, great info, thanks for posting. What a great thought to battle cyano with cyano, or to use it to combat the P problem.

    This thread seems to be also a subset of this conversation http://algaescrubber.net/forums/show...-won-t-go-away and you support my contention that this purported mechanism cannot explain rising P, which as you put it, is inevitable.

    It is wise to also note that the algae scrubber is not the only filtration system that experiences this - check out this product site and blurb:

    http://www.po4x4.com/Site/

    Maintaining the levels of waste products low while feeding your animals on a regular basis is essential for keeping invertebrates and fish in good health. In microbial well balanced aquaria, the two major pollutants are nitrates and phosphates. With current use of NP-Reducing BioPellets, it has become very easy to maintain nitrates and phosphate levels close to zero, however, in most tanks there is still a surplus of phosphates. Phosphate levels exceeding 0.03 ppm will negatively affect coral growth and higher levels will also negatively influence the health of your fish. In addition, high phosphate levels enhance the growth of annoying algae and cyanobacteria. Most of current phosphate reducing products are based on granular ferric hydroxide and leak iron-ions into your tank, which is enhancing algae growth and inhibiting coral growth and have a tendency to start clumping together, thus reducing its effectiveness.
    emphasis mine.

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    Quote Originally Posted by Garf
    Good read in that link. That's exactly the impression that I have been given after reading all the scientific stuff I could find on the subject. I find it amusing that he was totally ignored and people just carried on dumping stuff in their tanks.
    In the interest of full disclosure, I'm Totoro. The Pacific NW Marine Aquarium Society is the local SW fish club, and they're kind enough to tolerate my little lectures as I think through this stuff. And like I said, I've learned to stop quoting scientists... hobbyists, as you observed, generally don't dig that stuff.

    BTW, I think my analysis of EI dosing at the end of that post is wrong. I had just discovered Mr. Algae's page that day while I was googling for links to support what I had written, and I didn't read it closely enough to pick up on the "Buddy Ratio". I gather that's what you're supposed to use with the numbers from test kits (...obviously, I am not a graduate of the Redfield Ratio School of Algae Management).

    Still works, though: EI recommends NO3 from 5-30 ppm and PO4 from 1-3 ppm, so the upper bounds of the system (which I gather is where the cool kids hang out) perfectly correspond with the ideal Buddy Ratio of 10:1. Neat! Assuming "average" levels of 17.5 ppm NO3 and 2 ppm PO4, that's a Buddy Ratio of 8.75. Only at the low end does it go beyond the recommended Buddy Ratio range of 7:1 to 13:1. Either way, it appears that Mr. Barr empirically discovered how to manage algae by maintaining his tanks within the 10:1 to 22:1 window instead of reasoning his way there, but you can't argue with results -- especially considering that he got there first.


    Quote Originally Posted by Floyd R Turbo
    What a great thought to battle cyano with cyano, or to use it to combat the P problem.
    Biogeochemical cycling is what I find most interesting about the hobby -- which is to say, it's not that I'm so smart, it's just that I'm the lone oceanographer in a room full of marine biologists. But to give credit where it's due, it was IIRC a post somewhere in this thread about somebody having a bit of success bringing down P with intermittent skimming that was the trigger. I don't lurk here, but I do check in occasionally to see what you guys are up to, so I just saw that thread for the first time the other day... and intermittent skimming seemed interesting because bacteria are normally P-heavy, so if you let the population build up, and perhaps also have the good fortune to catch the skimmable fraction of bacteria at or near high points in their various boom-and-bust cycles, it seems plausible that you could remove a detectable amount of phosphorous. Then I thought, "Sure would be nice if there was some way to cultivate enough bacteria to do the job without turning the DT into bacteria soup."

    And then my head exploded. And then I felt like an absolute idiot for not having thought of it earlier, which to my mind is a pretty reliable test for the quality of an idea.

    Don't know if it'll actually work, but I'm just a theoretician, so I'm handing it off to the experimentalists so you guys can play with it.


    Quote Originally Posted by advertising blurb
    in most tanks there is still a surplus of phosphates
    I know many, perhaps even most hobbyists are skeptical about "Old Tank Syndrome" and the "DSB nutrient time bomb", but not only do I take phosphorous accumulation in the substrate for granted, I believe it is the key to the Standard Model of Aquarium Algae -- which I've been too chicken to post and instead kind of snuck onto the table to see if anyone would notice:

    Quote Originally Posted by 34cygni
    as the system's nutrient balance drifts away from 16:1, conditions will inevitably come to favor either cyano or green algae (...or diatoms if Si levels are high)
    So I guess I may as well pull the trigger...

    Let's start by reviewing algae in the natural world.

    It's well established that "typical" (the word being in quotes because, of course, there's no such thing...) freshwater temperate lakes experience an annual cycle of algae: in the spring, there's a diatom bloom; as the water warms, there's a green algae bloom; in mid-to-late summer, cyano takes over and remains the dominant form of algae until winter knocks back all primary production. The same pattern -- diatoms, green algae, and then cyano -- also occurs in tropical lakes, but there's no winter to reset the clock, so once cyano takes over, that's all she wrote.

    Sound familiar?

    Adriaan Briene, the Redfield ratio guy, got that the balance between cyano and green algae -- which is usually a phyto bloom in the wild, BTW, rather than green nuisance algae -- is governed by the N:P ratio. Most experienced hobbyists take for granted that low N favors cyano because it can fix its own nitrogen, and low N generally means low N:P ratio; green algaes must obtain their N from the water and cannot outcompete cyano for P unless there's enough N floating around, so high N:P ratios favor green algae.

    The missing piece of the puzzle is the Si:P ratio, because as far as diatoms are concerned, dissolved silica is a macronutrient. If you're curious, the diatomaceous Redfield ratio (actually the Redfield-Brzezinski ratio) is 106:16:15:1 -- that's C:N:Si:P.

    In a newly established aquarium, P levels are extremely low (though maybe not so much if you're using live rock or live sand from an established tank), so the N:P ratio will remain high for some time. This means green algae has the advantage, but diatoms will outcompete green algae for P at high Si:P ratios, so if there's any dissolved silica in the system -- not uncommon if unRODIed tap water is used for the initial fill before cycling -- then you'll get a diatom bloom.

    The diatoms will quickly deplete the system of Si (unless you keep adding more from the tap during top offs or water changes) and get eaten, 'cause everybody loves diatoms. This opens the door to green algae. Some aquarists do actually experience a greenwater phase, but most of us get green nuisance algae. This can potentially last for quite a while -- FOWLR and FW hobbyists, in particular, can tolerate rather high nitrate levels that keep the N:P ratio favorable to green algae.

    But eventually, P accumulating in the substrate will tip the balance to favor cyano. Cyano, however, is vulnerable to antibiotics, and hobbyists often kill it off, thereby opening the door to weird, P-loving, and very likely P-heavy algaes like BBA that were once consigned to obscure ecological niches but now plague hobbyists worldwide.

    So while the progression of algae types both in the wild and in aquaria is governed by P ratios, what changes these nutrient ratios to favor first one type of algae and then another is a bit different. In the wild, P ratios change by nutrient depletion: at high N:P and high Si:P, diatoms can bloom and will then draw down dissolved Si until they lose their competitive advantage over green algae; at high N:P and low Si:P, green algae can bloom and will then draw down N until it loses its competitive advantage over cyano; and then cyano goes to town. Diatoms will also go away in aquaria as a result of consuming Si until they can no longer bloom, but the transition from green algae to cyano is governed by P accumulation gradually lowering the N:P ratio, rather than N dropping because it's being consumed by primary producers. Though of course, very low or zero N is achievable with an ATS or in a heavily planted FW tank...

    I believe in this mental model because it is consistent with the available science and it has tremendous explanatory power, being able to account for decades of observations by hobbyists, a recent innovation in FW planted tank management, and the BBA plague in FW tanks, among other things. However, I acknowledge that it is only a crude sketch of a hugely complex and nuanced system -- as I said, I think this is the Standard Model of Aquarium Algae, not the Grand Unified Theory of Aquarium Algae.

    A true GUT would have to incorporate a host of variables I can't begin to account for. To be sure, P ratios are in the driver's seat when it comes to the competition between diatoms, green algae, and cyano, but what outcompetes what involves temperature, pH, lighting, flow, the presence or absence of grazers, and a host of imponderables ranging from dynamic ones like micronutrient ratios and unseen boom-and-bust population cycles in the microbial loop to "fixed variables" such as the actual cell sizes of the various algae species that are present in an aquarium (...because small algae cells have a high surface area-to-volume ratio and absorb nutrients from the water more efficiently, but large cells have more surface area, so they're able to capture more light).

    Algae scrubbers demonstrate that it's possible to push these secondary selection pressures so hard that you can actually override the governing N:P ratio, which is something the experimentalists should keep in the back of their minds as they explore the fringes of the hobby.

    And one final note: the Redfield ratio is a global average of a population average. A real oceanographer -- which I assure you, I am not -- would tell you that the Redfield ratio doesn't drive algae populations; rather, the local algae population drives the Redfield ratio.

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