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Thread: Nitrate limitation.

  1. #1

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    Nitrate limitation.

    I have just been reading about a reef keeper who has run an algae scrubber for 10 years. He said it has worked well, and the only long term problem was a build-up of phosphate. I suppose this would make sense if you follow the nutrient uptake ratio of 16 parts nitrate to 1 part phosphate used by algae. Is it reasonable to assume then if we dose nitrate to our tanks we can overcome this nitrate limitation and consume much more phosphate.

  2. #2
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    Not long ago there was already thread on exactly same topic. I am sure search will work for you well. I dont remember what final conclusion was though, but you can find some interesting ideas maybe.

  3. #3
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    You are correct, an ATS will remove nitrates faster than phosphates, and can lead to a big imbalance if not kept in check. There are many different ways to help avoid that situation, each person just has to decide which method works best for them.

    You can dose nitrates directly, you can rinse food well to remove as much phosphates as possible (this alone won't solve the issue, but will help), you can run GFO (you shouldn't need to run it 24/7/365 if your scrubber is working good, more like 2 days/weekend a month), you can dose lanthanum into a 10 micron filter sock, and I am sure there are a dozen other things one can do that would work that I didn't mention.

    Same thing can be said about DOCs. Even Randy Holmes-Farley was just speaking about the issue yesterday on RC.
    http://www.reefcentral.com/forums/sh....php?t=2138734
    I don't recall saying the ATS adds organics, although it might. Almost everything in the tank adds some type of organic matter. I was saying that an ATS alone will not remove it, and so the tank water will slowly yellow and potentially collect toxic organics over time without some means of exporting organics (GAC, skimming, Purigen, ozone, etc).

    This article details what I mean by organics:

    Organic Compounds in the Reef Aquarium
    http://reefkeeping.com/issues/2004-10/rhf/index.htm

  4. #4
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    He said it has worked well, and the only long term problem was a build-up of phosphate.
    This would not be "running well".

    an ATS will remove nitrates faster than phosphates
    No, it won't. N is removed at the same biological ratio as P. After all, it's being used to grow more biological material, and biological material follows the same ratio. If anything, algae can remove a bit more P if the pH is high, due to deposition of P onto the surface of the algal cells.

    The variable with P is rock, which continues to let off P, making it appear that P is not coming out of the tank as fast as N is.

    You can dose nitrates directly
    You don't want to dose anything.

    you can rinse food well to remove as much phosphates as possible
    99.9 percent of P is in the food itself; rinsing will not help. As soon as the food particles (or waste particles + urine) hit the water, you have instant DOC-food, way over and above the little bit of DOC-food that was in the liquid originally.

    GFO or lanthanum (and vodka/pellets too) will slow the scrubber down from doing it's job.

    Even Randy Holmes-Farley was just speaking about the issue: "I don't recall saying the ATS adds organics, although it might."
    This is basic biology 101. Hard to believe Randy would not know this. Of course algae adds particulate organics (algal pieces) and dissolved organics (vitamins, aminos, carbs, etc) into the water. That's what algae does. This is what feeds everything (the next trophic level) in the oceans and lakes. This is where DOC-vitamins and DOC-aminos come from, that corals have evolved to consume. I'm sure Randy was just thinking of something else.

    Randy: "I was saying that an ATS alone will not remove [organics]"
    Correct; algae does not remove organics. Algae adds DOC-vitamins and DOC-aminos instead.

    Randy: "so the tank water will slowly yellow"
    No, it won't. Yellowing is from dying algal roots. Besides, organics do not "build up"; they are consumed by bacteria and microbes just like in the ocean. Matter of fact, it's well known in biology that organics are the limiting factor in bacterial growth; this means that bacteria would grow more, if more organics were available. Since more organics are not available, the "level" of organics just stays at some equilibrium amount, usually, the same or less than the ocean.

  5. #5
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    I have read a lot about this as well and figure that when I acclimate coral or fish I will just replace the acclimated drip water with salt water mixed up the night or day(s) before. Most reefers don't impulse buy so it can be planned and if you don't buy anything for a while whats wrong with a water change once every year or so if it needs it because the phosphate has crept up a bit. Also I DIY all my food so that helps to. I figure it like this, you can only mimic nature in a miniature environment and adjust as we use to but, with the scrubber its so much easier and more natural. I have been scrubbing for more then a year and cannot detect this issue yet.
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    Quote Originally Posted by SantaMonica View Post
    No, it won't. N is removed at the same biological ratio as P. After all, it's being used to grow more biological material, and biological material follows the same ratio. If anything, algae can remove a bit more P if the pH is high, due to deposition of P onto the surface of the algal cells.

    The variable with P is rock, which continues to let off P, making it appear that P is not coming out of the tank as fast as N is.
    So, after reading some more, what are your thoughts on this thread Santa Monica? My experience certainly does not jive at all with what your saying, but this quote does exactly. N is never a problem for me, P is always something I need to work on in order to control (by means beyond just an ATS).

    http://www.reefcentral.com/forums/sh....php?t=2109768

    The various bacteria have different ratios of CNP. Further in addition to consuming N for growth, they use some more of it in anearobic respiration resulting in a a greater reductin in N via NO3 breakdown and N2 (nitrognen gas) releasing.

    These reactions will be different in different systems depending on a number of variables such as surface area, nutrient levels, type and amount of carbon source, ph and on and on.
    Keep in mind that the Redfield Ratio applies to total Nitrogen and total Phosphorous, not just inorganic nitrate and phosphate. Total carbon as well not just vodka or vinegar for example.

    Redfield Ratio: C:N:P = 106:16:1

    The Redfield ratio applies to a general average of all the microbial life found in the ocean, not just bacteria.

    Many bacteria can utilize organic forms of nitrogen and phosphorous when nitrate and phosphate are in low supply. Bacteria can utilize other forms of organic carbon as well.

    This can make the use of the Redfield Ratio in a reef tank almost useless, but does let us know that bacteria utilize a lot more N than P to grow and reproduce.

  7. #7
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    This is the way I look at it...

    With the amount of P added in fish foods alone & excreted by fish, it is possible that this source may provide ample P to reduce the nitrate levels, if enough fish food is added.
    Especially with the extra food put in by a scrubber. Plus, I've seen hundreds of scrubber-only tanks with unmeasurable N and P. I'm sure you could create a special situation where there is some kind of limitation, but have not given it too much thought.

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    Hmmm... conditions that may favor a higher reduction in nitrate vs phosphate that my system has that most others do not... DEEP SAND BED. My sand bed has anaerobic areas out the wazoo.

    I guess my point is, an ATS will remove N/P at the redfield ratio, and bacteria in our tanks for the most part will as well, but in some tank conditions bacteria live in anaerobic areas and consume more N than P which will lead to a skewed ratio within the tank. Since my entire display has a deep sand bed I bet I have a much larger than average area of anaerobic conditions.

  9. #9
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    Yes but the consumption of N will stall when the values are low; the consumption does not continue. Then another feeding flushes it all out, and gets it going again.

    Kind of like if you sealed off a room and tried to remove all of the oxygen; as soon as you open a door or window the ratios are going to be right back to where they started.

    In the end, you can't remove more N than P, or more P than N. Everything removed has to equal what is put in.

  10. #10
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    I suppose then my probem (I've never seen 0.00 on the hanna Phos meter) is that there is a large amount of established LR in the system that is performing denitrification. Before I put the scrubber on, I had lowered the N from 160 to 20 and the rock and skimmer took it the rest of the way down w/o any further PWCs, at that point, P was a problem and I kept it at bay with RowaPHOS for a short period of time. I guess that is the only thing I can think of that is causing the P > 0 issue for me 'cause N has never been a problem since I took over maintenance on this tank.

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