# Does pearling mean the water is oxygen saturated?



## DaveWatkin (11 Feb 2021)

This might be a stupid question but I'm reasonably new to co2 and always concerned for my livestock.

Common sense tells me that regardless of co2 level in water (it's below 30ppm) if plants are pearling then there is enough oxygen in the water right? 

I have nice even flow but not much surface agitation right now as still trying to find the right balance. 

Going to add floating plants to fix the issue once I can get hold of some.


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## ceg4048 (11 Feb 2021)

DaveWatkin said:


> This might be a stupid question but I'm reasonably new to co2 and always concerned for my livestock.
> 
> Common sense tells me that regardless of co2 level in water (it's below 30ppm) if plants are pearling then there is enough oxygen in the water right?
> 
> ...


Hello,
        I'm not really sure I've interpreted your question correctly but it sounds as if you're asking whether the amount of dissolved CO2 displaces the dissolved Oxygen. The answer is no.

The other part of your question seems to be whether pearling is an indication of sufficient dissolved oxygen. The answer again is no. Pearling is a phenomenon that _can _indicate high dissolved oxygen levels, however because it is dependent on a couple of variables it is not necessarily a consistent indicator of good so-called balance.

Regardless of the level of dissolved oxygen in the water it's very easy to annihilate your fish with the plants happily pearling along, so this is a very poor metric to determine tank health.

Cheers,


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## tiger15 (11 Feb 2021)

I would say yes.  Pearling can occur only in water saturated with oxygen.  You don't need the whole water volume to be saturated, just locally adjacent to the leaves.  

Saturated oxygen concentration is temperature and TDS dependent as shown.  At 25C, saturated oxygen is about 10 mg/l.


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## Easternlethal (12 Feb 2021)

The idea that oxygen is affected by other things in water comes from what is called the diffusion coefficient which is a formula to measure how quickly it diffuses (and hence escapes). 

This diffusion rate is, in turn, affected by viscosity, which for our purposes measures the ability of the water to hold oxygen molecules due to how much other 'stuff' is in the water, which is also affected by how much pressure there is, what is the temperature and so on (because oxygen is a 'light' molecule and always tries to reach an equilibrium with the amount in the air).

Pearling is just oxygen diffusion in action as o2 escapes to find its equilibrium with the air but it isn't evidence of how much oxygen is actually inside the water (which depends on viscosity).

Viscosity is why some people think that co2 displaces oxygen but in reality both are 'light' molecules and easily displaced by other things which occupy more 'space' in the water.

Water can carry both co2 and o2 (as well as other gases like nitrogen) but it's the 'heavier' molecules like bacteria, micro organisms and other microbiological processes taking place in the water as well as things like pressure and temperature that have a far greater effect on their displacement.

Not sure if this helps but might be of interest to some.



Sent from my LM-V405 using Tapatalk


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## dw1305 (12 Feb 2021)

Hi all,


ceg4048 said:


> Regardless of the level of dissolved oxygen in the water it's very easy to annihilate your fish with the plants happily pearling along, so this is a very poor metric to determine tank health.


You can get pearling in sewage works (during <"activated sludge treatment">), if it is sunny. The process involves period of intense churn and then a static phase to allow the solids to settle out. During the settlement phase flocs containing cyanobacteria are buoyed to the surface by their oxygen production.

You might also be interested in <"Canford Park"> which had some <"very interesting water parameters">.


DaveWatkin said:


> if plants are pearling then there is enough oxygen in the water right?


As the other have said, you can still asphyxiate your fish. The reason is that oxygen isn't particularly soluble, <"but CO2 is">.

Because the haemoglobin/haemocyanin in <"fish/shrimp blood"> transports both oxygen and CO2, high CO2 levels in the water will stop oxygen diffusing back into the blood stream.

cheers Darrel


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## DaveWatkin (12 Feb 2021)

Thanks guys. I know I can still kill the livestock even with O2 saturation if I add too much CO2. They don't cancel each other out and are two gasses in the water at their own separate levels. Pretend I never asked about CO2 as it adds confusion. My CO2 levels are low and my temp is around 20-21 Celsius. 

Basically I was just wondering if plants pearl because the water column can't take any more O2 (in that particular place obviously but in this example flow is good and pearling is across a whole carpet) or if they could still pearl even with low O2. Read conflicting information online. Basically wondering if it's a good sign and one less thing to worry about as like I said I currently don't have much surface agitation and am waiting on some floating plants.

I don't have a film and I change water every two days currently. Tank is an open top rectangle type so there is a good surface area anyway without waves but I know it can always be better.


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## Zeus. (12 Feb 2021)

tiger15 said:


> I would say yes. Pearling can occur only in water saturated with oxygen. You don't need the whole water volume to be saturated, just locally adjacent to the leaves.



Yes, if plants are not pearling turn the filters/powerheads off and pearling starts


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## Zeus. (12 Feb 2021)

DaveWatkin said:


> Basically wondering if it's a good sign and one less thing to worry about as like I said I currently don't have much surface agitation and am waiting on some floating plants.



I went OTT with light with a little experiment, left side in pic getting lots more light than right.



Pearled like mad, then plants got pinholes then melted.


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## dw1305 (12 Feb 2021)

Hi all,


DaveWatkin said:


> Basically I was just wondering if plants pearl because the water column can't take any more O2 (in that particular place obviously but in this example flow is good and pearling is across a whole carpet) or if they could still pearl even with low O2.


I think if the whole carpet was pearling it would suggest that the water column is close to oxygen saturation. As the others have said oxygen isn't very soluble in water, so localised pearling just tells you that the water in contact with the leaves was fully saturated.

It is that lack of solubility that leads to the <"Canford Park"> example earlier in the thread.



dw1305 said:


> ......... I had an interesting one today. I won't tell you the location, or context, but it was a pond and the water sample had a dissolved oxygen level of 180% (~20oC, 18mg/L DO) and a pH value of pH 10.5................





dw1305 said:


> .......... about <"20 m long, 5 m wide, entirely surrounded by paving"> and around 60 cm deep. We sampled it pretty much at midday, and it was calm and sunny. The pond was even greener than the photo, and a couple of fairly unhappy goldfish were just visible, hanging under the water surface.
> 
> When we sealed the water collection bottles (collected with a <"Phil sampler">) the green water algae were pearling very noticeably.......



cheers Darrel


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