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Pearling vs. O2 saturation

Discussion in 'CO2 Enrichment' started by Oreo, Jul 20, 2010.

  1. Oreo

    Oreo Guru Class Expert

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    I've seen a lot of comments on this lately saying that pearling doesn't happen till the water column reaches O2 saturation. Has anyone actually tested dissolved oxygen levels relative to pearling? I'm betting not. And I have another hypothesis of what causes pearling that makes more sense (to me anyway.) Seems that this could be tested easily enough though. Dissolved oxygen tests aren't particularly expensive.

    My theory is that pearling has nothing to do with the water column reaching O2 saturation. Instead, pearling is simply a product of a plant producing oxygen faster then it can dissolve in water. Unlike CO2 which is easily & quickly dissolved, O2 isn't taken up as quickly or easily. If I stick an air tube into a bucket of water & pump O2 through it you wouldn't suggest that the water column has reached saturation just because there are bubbles coming from the tube. Similarly, I can start & stop pearling in my aquarium just by controlling the light intensity. Within a couple minutes of doubling the light the plants start bubbling. Turn the light off & the bubbling stops in a couple minutes. It's reliable & repeatable.

    Just thought I'd take a second to question some "common" wisdom on pearling.
     
  2. ShadowMac

    ShadowMac Lifetime Members
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    Interesting observation. It would be interesting to see O2 sat. data along with observed pearling and light intensity. Need some fancy equipment for that...PAR meter, O2 sat. meter (not cheap), and eyeballs (come pre-equipped with most standard aquarists). Sometimes i question if some of my plants are pearling and its not just the collection of CO2 mist on leaves. How can I tell the difference?
     
  3. Tom Barr

    Tom Barr Founder
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    I agree, pearling is more a function of the rates of growth.
    O2 saturation has little, if anything.........to do with it.

    O2 is not very soluble.

    At higher rates of growth, the O2 bubbles form, this can occur in non CO2 tanks as well, flow play a large role also in seeing it.

    Still pearling is a not a bad sign.
    It might not show that good growth is still occurring if pearling is lacking............but, having it can often give the gardener a good indication of good growth.
    An O2 data plot vs time during the lighting cycle would be better.

    Test kits are cheap, but a meter with data logging is much preferred for O2.

    Regards,
    Tom Barr
     
  4. Tom Barr

    Tom Barr Founder
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    O2 meters do not detect O2, likewise, CO2 meters do not detect O2.

    Regards,
    Tom Barr
     
  5. ibanezfrelon

    ibanezfrelon Guru Class Expert

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  6. dutchy

    dutchy Plant Guru Team
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    I agree with that. Personally I think that the whole "pearling" thing is overrated a bit. Since I dropped down to 55 to 60 PAR at the substrate, pearling is virtually non existent. Just a bubble here and there. Yet I have very good growth, some plants are like weeds and look better than before.

    What about the following hypothesis: "Pearling is the consequence of too much light"

    regards,
    dutchy
     
  7. Tom Barr

    Tom Barr Founder
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    There could be several things happening:

    1. Massive flow and exchange during the water change, all boundary layers have been disturbed and "cleaned".
    2. All gas, CO2 included, can enter the plants' aerenchyma. Then later, leak out.
    3. More CO2 is added than normal and plants take up a lot of CO2 temporarily. This allows more growth for a short burst.
    4. Tap water can have high CO2 and is often under pressure and cooler, then releases the CO2 and O2 at highe rrates than normal.
    5. More O2 is added, which can release more CO2 by respiration of bacteria.

    Likely a bit of all these.

    Not certain or how we might isolate each either.
    You can do water changes and save the old water and add it back again.
    That would address the temp and richer CO2/O2.

    Regards,
    Tom Barr
     
  8. Oreo

    Oreo Guru Class Expert

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    Tom, I think we could boil it down one step further. Pearling is a function of the rate of photosynthesis.
     
  9. Tom Barr

    Tom Barr Founder
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    Well, pearling occurs based on the rates of growth and flow.
    Less flow= more pearling
    Less light= less growth= less pearling
    Anything that reduces growth rates should also reduce pearling.

    Regards,
    Tom Barr
     
  10. dutchy

    dutchy Plant Guru Team
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    Ok, so let''s take this a little bit further...

    So if what we want is a high flow, low light tank, that means almost no pearling...

    next step...

    Pearling is a sign of low flow, too much light or a combination of both.

    next step....

    Pearling is BAD :) :) :)
     
  11. Oreo

    Oreo Guru Class Expert

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    I think that's taking it a couple steps too far Dutchy.

    Define too much light? Higher light causes faster photosynthesis which results in plants putting out more O2, but if there is sufficient CO2 & nutrients to support healthy growth at that light level then that amount of light isn't too much even if the result is pearling.

    Similarly with flow, you can have enough for healthy growth & still have pearling.

    Pearling on it's own isn't bad.
     
  12. dutchy

    dutchy Plant Guru Team
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    Hi Oreo,

    I wasn't being very serious, hence the :) :) :)

    Sorry if I gave that impression, it wasn't my intention to start a serious discussion.

    regards,
    dutchy
     
  13. ShadowMac

    ShadowMac Lifetime Members
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    Tom,

    What does an O2 probe measure? just curious since you mentioned this. Something like an O2 sat meter for blood...it doesnt actually take a sample of blood to give its measurement.
     
  14. Tom Barr

    Tom Barr Founder
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    Could........depends on what metric folks want to use.
    I prefer high flow low light combos.

    Good for fish and plants.

    Also, whar occurs during a water change that is NOT normal? We shut off the filters and water movement. This allows the O2 to build up and appear visible.
    This takes a few minutes to drain and fill an aquarium, so there's NO flow or very little...........plenty of CO2, light, folks often dose after.........

    So many things consipire to increase pearling after a water change.

    Regards,
    Tom Barr
     
  15. Gilles

    Gilles Lifetime Members
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    [video=youtube;npFOKeH9hlU]http://www.youtube.com/watch?v=npFOKeH9hlU[/video]
     
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