Overskimming

Discussion in 'General Discussions and Advice' started by Warr7207, 22 Feb 2008.

  1. Warr7207

    Warr7207

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    Hennie, please can you gives us your thoughts on this exact below:


    "Myth 17: You can never skim a tank too much.
    Yes, you can. Far too many works have dealt with various aspects of protein skimming. I still feel there is too little information on exactly what, how much, and how effectively foam fractionation affects various components of the water column of reef aquaria. For the most part, protein skimmers are employed as water quality control devices to maintain low levels of organic and some inorganic materials, notably compounds containing nitrogen and phosphorous commonly linked to degraded water quality not conducive to the growth of many reef species such as corals. Whether or not they are used secondarily for other questionably useful purposes such as elimination of toxins or increasing oxygenation is another matter. My point is that once nutrient levels are low and conducive to a healthy aquarium, and until other secondarily important aspects of protein skimming are experimentally validated and quantified, any skimming over that required to maintain low levels of organic and inorganic pollutants is overskimming. Why? Because if the water is cleared of those things that are detrimental, it is also likely to be equally cleared of things that are beneficial. Given the now well-recognized limitations of providing large amounts of food without a corresponding decrease in water quality, skimming as little as possible while maintaining the aforementioned high water quality is only pragmatic. There is no advantage to a constantly stripped water column in all but a very few specialized situations.
    If I were asked what a solution might be, I would propose the following. Use the most efficient skimmer possible and one that is capable of maintaining high water quality when used constantly. Assuming that they do provide some amount of oxygenation, even if minimal, I would then begin shutting off the skimmer during the day for a few hours and measure tank condition visually and through testing for several weeks. If water quality is maintained, I would increase the number of hours the skimmer is off, and wait again, continuing this process until the maximum number of hours is reached where water quality and tank health remains the same without the use of the skimmer. I would also opt for daylight discontinuance since oxygen is less of a problem when photosynthesis is occurring, and since most aquarists tend to feed fish and other products like phytoplankton during the day. This way, residual foods will not be removed for at least several hours. Some aquarists may even find that they can discontinue skimmer usage entirely (I think this likely, especially if activated carbon is employed).
    Potential: Minimal to serious. In the best cases, continuous skimming results in relatively healthy tanks that are considered successful by most standards. In the worst cases, organisms perish because of the lack of available foods in the water column. In most cases, the results are a "sterile" looking tank with little alive but corals and coralline algae. Corals tend to appear weakened and, for lack of a more accurate description, not robust.
    Distribution: Extremely widespread. There are many who employ alternate means of tank filtration, and these are usually the same people who appreciate the obvious differences in allowing more material to remain in the water column without compromising water quality. Foam fractionation use is both desirable and extremely widely employed, but as with other things should be employed properly and with a judicious purpose."



    Source: Mything the Point, Part Three: Conclusion - Reefkeeping.com
     
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  3. sihaya

    sihaya

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    I've never been too sure what to make of the above myself. It seems mostly assumptions/conjecture rather than "fact." I've never seen any real evidence/research that would clearly support the notion that you can over-skim a tank any easier than you could "over-filter" a tank... but that doesn't mean you couldn't.

    So, anyway, I did the best I could and asked one of the few existing protein foam fractionation experts in the country/world. Here's a list of the questions I asked him and the answers and his graduate student gave me:
    www.asira.org - Protein Skimmer Q&A
     
  4. Reef Maniac

    Reef Maniac MASA Contributor

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    This is an excellent article (like most of Eric Borneman's writings...) and I agree in principle with what he's saying.

    Sara's "skimmer expert" is mostly correct as well, but I disagree with his statement:

    I have looked at skimmate through my microscope on many occasions, and can state that there has been a great amount of single cell algae (phytoplankton) and microscopic animals (zooplankton) in every drop of skimmate I have examined.

    Eric's concern here is clearly that "overskimming" will remove beneficial "things" from the water. IMHO this is not the removal of any chemical (such as iodine), but rather the removal of the micro algae and other small life forms (such as larvae of bristleworms and copepods...) which could become food for corals and other critters living in our tanks.

    Here I must disagree. Most (all?) skimmers only produce a decent skimmate after running for a few hours, and this "lag" time is increased if the "sludge" in the skimmer neck dries out - I really cannot see how this "stop/start" skimming can work well.

    The obvious solution is to allow for some of the tank water to bypass the skimmer. This happens in any case where a skimmer is installed in a sump, or where it hangs on to the tank. The only risk of really over-skimming, IMHO, is where (such as in my tank...) the overflow water is plumbed to flow through the skimmer before entering the tank - and in such a case it is very simple to allow a "bypass" through a second downpipe to flow directly to the sump. The volume of bypass water can then be regulated to achieve the same objective.

    This is the crux of Eric's message, and I totally agree :thumbup:

    My personal opinion is that in 90%+ of our tanks over-skimming is not an issue (or even possible...) because of the size and/or location of the skimmer. The other 10% of us can easily adjust our systems to prevent over-skimming, if it becomes a problem.

    Hennie
     
  5. sihaya

    sihaya

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    Yes, I have heard/read that many people have observed this (that they've seen the bacteria, etc. in their skimmate). But my question is, how do you know the difference between what your skimmer pulls out and what GROWS in the skimmer off of what the skimmer pulls out? Bacteria can grow really fast.

    ALSO... I do think some bigger things are "pushed" up on the mass of bubbles. But I'm not so convinced it's in significant quantities. Some drops of water are bound to get pushed up with the bubbles and those drops could have plenty of bacteria, phyto, etc.

    IMO, It would be most helpful to know if 1) what's growing int he skimmer vs. what's being pulled out, and 2) what the concentrations of these bacteria, etc. are, in the skimmate vs. in the tank water. If the concentrations are the same or similar, that would mean to me that the skimmer isn't actually pulling them out (not to any significant degree).
     
  6. Reef Maniac

    Reef Maniac MASA Contributor

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    Algae need light to grow - the skimmer cup is mostly in total darkness, so algae growth in the cup would be minimal.
     
  7. sihaya

    sihaya

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    Hmm... minimal, sure, but still existent. And again, even if it's not growing in the skimmer, it may be getting caught in the "droplets" pushed up by the bubbles. To me, the real question is not if algae and bacteria are present, but in what *concentrations* they are present. Is it significant? Is it more or less than that of the water column? Honestly, I'm just asking questions. I don't know anything for certain. But that's my point. I'm just not ready to assume that skimmers pull out these things in significant quantities. Thus, since I don't know, I'm inclined to trust Dr. Tanner's professional opinion on the matter... until maybe some clever hobbyist(s) come up with a better way to test these things. And actually, I think there are... or were, a group in NYC attempting it. I don't know where they are with the project now though.
     
  8. Kanga

    Kanga Retired Moderator MASA Contributor

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    My idea of overskimming at a mere 15.734,92 € :D


    [​IMG]


    Ok seriously, what are the chances that an average reefkeeper will be able to overskim, and how would it affect my tank?
     
  9. sihaya

    sihaya

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    Kanga- as you can see, this is a "controversial" topic in reef keeping. Even Borneman and Calfo clearly disagree. Borneman says you can easily skim too much, Calfo seems to think you could never skim too much. It's just one of those topics on which many intelligent people disagree. You'll have to read the different articles/discussions written about it and just decide for yourself. :)
     
  10. Reef Maniac

    Reef Maniac MASA Contributor

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    Quite slim

    Less small critters - thus potentially less food for the corals. Unless a skimmer is totally oversized, AND there are other negative factors, I don't think it would SERIOUSLY affect one's tank. On the other hand, IF you are trying to keep the system as natural as possible, and IF you want to reduce nutrient input as much as possible, it could be beneficial to reduce skimming.

    I guess it all boils down to whether one wants a "naturally balanced ecosystem" or an "engineered ecosystem" - both will probably give the same end result if you're only looking at keeping fish and corals, but the "natural" system will most likely be able to support a much larger bio diversity, and allow one to (possibly?) successfully keep some of the more difficult-to-keep animals, such as gorgonians and sea apples...

    Hennie
     
  11. Reef Maniac

    Reef Maniac MASA Contributor

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    Exactly - and it is this skimming out of phyto- and zooplankton which is bothering the proponents of more natural "ecosystems".

    Looking through a microscope it is *much* more concentrated than in the water column - and yes, I (and Eric Borneman...) think it IS significant.

    I must say, this is the first time that I've heard of him (or her ???). Is he active in the hobby, has he published anything marine aquarium related - I'm always keen to "discover" new experts :)

    Hennie
     
  12. sihaya

    sihaya

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    Again, not to repeat myself too much, but it's not if they're being taken out that I think is important... it's in what *concentrations* they are being taken out. Even if they are being pulled out (and that's still an IF in my mind), this might not necessarily be a bad thing if the concentrations being pulled out aren't enough to harm the "ecosystem."

    And in fact, how are we so sure that it's not actually beneficial to have some bacteria and phytoplankton pulled out from the water column? In the wild, there are lots and lots of filter feeders which pull these things out. Do our tanks have this same proportion of filter feeders? I doubt it! And (imo) that's part of the problem with trying to "be natural" with our systems. We're never going to have in our tanks the balance of organisms at different places and levels of the food chain that exist on the natural reefs. So, really, there's just NO comparison. We have to come up with some other way(s) to think about "balance"... ones that work for captive systems.

    But again, I still suspect there's a very good possibility that these things are growing in the skimmer. Not all (or even most) skimmers block light. Most the ones I've seen are actually quite clear. I know that you and Mr. Borneman and many other highly intelligent reef keepers think it is significant... while at the same time, Mr. Calfo and Bob Fenner and many other equally intelligent people seem to think it's not significant. I'm personally "undecided." But my point is that this is an issue on which intelligent people can and do disagree. So my questions are aimed at getting to the "root" of the disagreement. What do we need to know to settle this issue? Is there anyway we can do tests or trials to figure it out?

    Dr. Tanner isn't an aquarist, but his graduate student is... that's why they answered the questions together. However, aquarist or not, I'm confident that Dr. Tanner likely knows more about protein foam fractionation than anyone in the aquarium hobby. It's his life's work/career to study this. :)

    But Hennie- I'm not necessarily disagreeing with you here. In fact, I don't run my skimmer much at all (partly because I do wonder what it might be pulling out that I don't want it to). I'm more or less just playing "devil's advocate" here because I'm honestly undecided. I just don't think we know enough yet to say one way or another with any real conviction.
     
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  13. Reef Maniac

    Reef Maniac MASA Contributor

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    Well, don't believe me - take a microscope and look for yourself...

    Don't twist what's being discussed here - NOBODY said that it's a bad thing to remove "concentrations" of bacteria and phytoplankton - it's obviously NOT a bad thing under normal circumstances. Remember, this discussion is NOT about whether skimming is good or bad - we all agree (I'm sure) that skimming is beneficial (VERY beneficial in my opinion...), this discussion is about whether OVER SKIMMING could be detrimental...

    To repeat one of Eric's originally quoted statements:

    Based on personal experience, I don't agree. My tank is skimmed with a Deltec AP902 skimmer, coupled directly into the tank overflow. This skimmer is located in a small room next to the sump. This "sump-room" only received about 20 minutes of direct light (1 x 36W PC...) per day, when someone enters the room and switches on the light, and although there is *some* reflected light which makes it's way through the (heavily encrusted by coralline algae) side glass of the tank, this is blocked from entering the skimmer cup by the black plastic skimmer cup lid. I can safely say that the skimmer receives less than 5% of the light shining in the tank, and it is highly unlikely that algae would grow/proliferate to any meaningful extent under these conditions.

    Of course, it should be very easy to prove (or disprove...) your argument: Take a plastic container (or even an old skimmer cup), place some tank water in it (about the same volume as the skimmer removes within 24 hours), add some plant fertiliser if you like, and place it next to the skimmer - if your theory is correct the water in the container should be full of algae within a few hours... and this would be skewing the "experiment" towards the algae growth, as the water in the skimmer cup would actually have increased at a gradual rate over the time span of the test - the actual average photo period for the water in the skimmer will only be half the time the water in the test container would have been illuminated.

    That sounds like lawyer (or politician...) talk - here in the real world we either disagree, or we don't :whistling:

    Anyway, I'm afraid that we're tacking away from the original discussion - Can one over-skim a tank... As stated previously:

    Hennie
     
  14. Shaun

    Shaun Retired Moderator

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    All I will say, if my skimmer can remove flying ants, it can remove all sorts of other things.
     
  15. Warr7207

    Warr7207 Thread Starter

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    Hi Hennie

    I have an external skimmer so all the return water goes through the skimmer, I have a skimmer bypass pipe.

    Should I have the bypass pipe allow a small amount of water go directly to the sump, just in case ?
     
  16. DragonReef

    DragonReef

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    This is indeed an interesting topic, and one worth discussing.

    I think the reason this question is always open to debate though is because in most instances it's asked in such a broad sense. " Is it possible to overskim our tanks ? "

    I feel the question should be more specific.

    " Is it possible to overskim my softy / zoathid species tank ? "
    " Is it possible to overskim my SPS / Reef Crest simulation tank ? "

    IMO its a situation of Horses for Courses. In setting up our tanks, we try in most instances to replicate a reef zone and the species that are found in those zones. Some aquarists try for a Reef Garden with a mixture of species. The latter I feel the most difficult to achieve succes with, as what you compromise for one is at the detriment of the other.

    For all intents and purposes though and back to the question. If I were to setup a species specific tank for Mushrooms / Zoanthids / Elegance corals etc I would look to find a skimmer that would adequateley maintain water quality. In other words a skimmer rated for that 400 litre system, if thats the size tank I was using for this. I would also be midfull of the fact the the fish load for this system should be within acceptable stocking levels for the size of the tank. Why ? Because I would be doing these types of corals a disservice by skimming the water to within an inch of it's life with a skimmer rated 4 or 5 times bigger than the volume I have. These types of species fare better in water slightly richer in nutrients.

    On the other hand, If I was to setup a system concentrating on SPS type corals, it's a different scenario for all the opposite reasons and I would look to skim as much as I possibly could.

    Even in both these scenarios the variables are always there and dependant on the aquarist's skills, husbandry techniques etc. In truth these are all closed systems and as such the water is constantly being polluted. The possibility of actaully overskimming in each scenario is very slim.

    JMHO :D
     
  17. sihaya

    sihaya

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    Fair enough... but this still begs the same questions. What would the skimmer be pulling out in concentrations so high as to be detrimental? Bacteria and phytoplankton? Ok, maybe, but even so... how do we know how much is too much?

    And that's enough for many types of algae and bacteria. In fact, some algae can survive and multiply without hardly any light at all.

    Hmm, interesting idea, but I don't think this proposed environment would be sufficiently analogous to that in a skimmer. But I'm sure it could be tweaked to make it more analogous. Definitely something to think about...


    No, not at all. You're of the opinion that yes, one can over skim a tank. I'm of the opinion that we don't have enough information to say one way or the other. So I'm not saying I think you're wrong... I'm just saying that there are equally good arguments/points from the other side.

    Yes, this is what we are discussing. Can we over-skim? I don't know... and have yet to see conclusive evidence one way or the other.
     
  18. Mekaeel

    Mekaeel Moderator MASA Contributor

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    thank you Anthony.i was also looking at it from that point of view
     
  19. sihaya

    sihaya

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    Even easier... just don't keep your skimmer on 24/7. This is what I do to avoid "over-skimming" (even though I'm not convinced such a thing is possible, better safe than sorry, right? ;) ). I only keep my skimmer on about 12hrs/day or less. And I keep it off for at least several hours after feeding the tank. This is actually what I've read/heard Borneman suggest on several occasions too.
     
  20. Warr7207

    Warr7207 Thread Starter

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    Not so easy. Easier to have a small % bypass the skimmer, if it has the same effect and not have to worry if the skimmer is on/off.
     
  21. IMarine

    IMarine

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    Hi friends i dont think that you could over skimm your tank i am running a bubble master 250, 24 7 on my 1500mt tank and it removes a lot of shit rotten smelly gunk
     
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