Pearling vs. O2 saturation

Oreo

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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.
 

ShadowMac

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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?
 

Tom Barr

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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
 

Tom Barr

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ShadowMac;53199 said:
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?

O2 meters do not detect O2, likewise, CO2 meters do not detect O2.

Regards,
Tom Barr
 

dutchy

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Tom Barr;53201 said:
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.
Regards,
Tom Barr

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
 

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ibanezfrelon;53203 said:
This is a very interesting subject to me.
Years ago there was a sharp discution about this betwen Tuljan (Akvarij Net expert and Barreport lifetime charter member) and Brainman...
The question was later asked here http://www.barrreport.com/showthread.php/2571-Question-about-pearling?highlight=tuljan

To me this question stays unanswered: why does intense pearling happen just after large water change?

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
 

Oreo

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Tom Barr;53201 said:
I agree, pearling is more a function of the rates of growth.
Tom, I think we could boil it down one step further. Pearling is a function of the rate of photosynthesis.
 

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dutchy;53204 said:
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

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
 

dutchy

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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 :) :) :)
 

Oreo

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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.
 

dutchy

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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
 

ShadowMac

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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.
 

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dutchy;53212 said:
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 :) :) :)

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