# why have my plants stopped pearling?



## tyrophagus (26 Apr 2010)

So my 180l tank is 6 days old and for the first 5 days I did at least a 50% water change. Back at work today so today was the first day with no water change. CO2 addition at about 8 drops per sec. C02 yellow. Add 10 mls easycarb a day plus Ada brighty k.  My lighting is on for 8hrs with the middle 4 hrs at the brightest but still only at 50% output from TMC LED lighting tiles x2. 40cm above water and tanks 45cm deep. 

Every day so far the plants have been pearling except today.  Checked tank during peak lighting and not a single bubble of oxygen on any plant. 

Do I need to increase lighting intensity?

Do you think previous pearling was due to water change.?  Would seem that way as the other parameters have remained constant.  Why would this happen.


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## nry (26 Apr 2010)

Pearling could have just been from the fresh water and the extra CO2 and oxygen content...


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## LondonDragon (26 Apr 2010)

They were pearling because of the water changes, water changes produce a "false pearling" because when you perform a water change the 02 reaches maximum concentration.


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## tyrophagus (26 Apr 2010)

So do I worry about the plants not pearling?  As the tank is new and not cycled I assume increasing the lighting is a bad thing as with all the ammonia present it will just cause algae. 

Is pearling essential to indicate photosynthesis?


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## ceg4048 (27 Apr 2010)

LondonDragon said:
			
		

> They were pearling because of the water changes, water changes produce a "false pearling" because when you perform a water change the 02 reaches maximum concentration.


Actually the pearling is real, not false. When you do a water change and the plants are exposed to atmosphere they absorb high levels of atmospheric CO2 in the exposed tissues. New water is also high in CO2. Therefore the high net values of CO2 enable better photosynthesis. In a way therefore this is an indication that you do not have optimum CO2/flow.



			
				tyrophagus said:
			
		

> So do I worry about the plants not pearling?


No, it would be better to worry about whether you have decent plant health and decent growth.



			
				tyrophagus said:
			
		

> As the tank is new and not cycled I assume increasing the lighting is a bad thing as with all the ammonia present it will just cause algae.


Thank you. A Most Excellent Assumption.  



			
				tyrophagus said:
			
		

> Is pearling essential to indicate photosynthesis?


No. Pearling is a phenomenon of environmental conditions, not a prerequisite for plant health. If you wish, add more CO2, which will generate high O2 levels, will therefore more likely generate more pearling, will increase growth rates, will require more nutrients to sustain the growth rates and will require high maintenance effort due to higher levels of generated organic waste.

Cheers,


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## tyrophagus (27 Apr 2010)

Thanks everyone. I'll stick to the plan then, just have to be patient. My plants are growing and look healthy but it's early days.


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## chump54 (27 Apr 2010)

Hi Graeme,

you might already be doing it but it's a good idea with a new tank to keep doing water changes. say every other day. If not everyday to start off with, for a couple of weeks.

Chris


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## dw1305 (27 Apr 2010)

Hi all,
The pearling is just because the water has become fully saturated with oxygen, at this point no more oxygen can go into solution, and the bubbles of O2 are out gassed. The pearling happens because the oxygen comes from a series of "point sources" on the plant leaf (the stomata), and the bubble nuclei will grow until it gets large enough so that it's volume of gas exceeds the "stickiness" of the leaf surface (just like bubbles of CO2 in a pint glass of Lager come from imperfections in the glass surface, or from the peanut that you mate threw in why you weren't looking). 

Whether you get pearling or not depends upon a variety of factors, the most important being that O2 is the "waste" product of photosynthesis 

 and that oxygen is more soluble in cold water. 

With abundant carbon and light energy a plant can be photosynthesising at somewhere near it's maximum productivity, but pearling would still not occur if other oxygen consuming processes (respiration or decomposition, the conversion of NH3 to N03 etc.) mean that the water does not become fully saturated with oxygen.

cheer Darrel


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## paul.in.kendal (28 Apr 2010)

dw1305 said:
			
		

> ... and that oxygen is more soluble in cold water.


Does that mean one can increase the likelihood of pearling by increasing the water temperature, because warmer water becomes O2 saturated more quickly?


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## peter1979 (28 Apr 2010)

paul.in.kendal said:
			
		

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I think the problem here lies that when you increase the temp of the water CO2 is less soluble in the water as well, so this in turn effects the rate at which photosynthesis occurs as well as the levels of O2 in water.


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## paul.in.kendal (28 Apr 2010)

peter1979 said:
			
		

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...so no such thing as a free lunch, then!

I started out thinking pearling was massively important, aesthetically.  I get hardly any pearling now - but my plants are really healthy - so I've decided that the excitement of pearling I can do without!


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## dw1305 (29 Apr 2010)

Hi all, Paul.in.Kendal wrote 





> I think the problem here lies that when you increase the temp of the water CO2 is less soluble in the water as well, so this in turn effects the rate at which photosynthesis occurs as well as the levels of O2 in water.


  This is true:

Another factor is that CO2 is more soluble in water than O2:
At sea level, at 27oC, pure H2O is saturated with 7.9 mg / l O2, but with only 0.42 mg / l CO2 (this is because of the low atmospheric content of CO2, if you add it (see the graph) you can add a huge amount of CO2), and the solubility/ temperature curves differ.






Oxygen solubility in pure water at mean sea level.
Temp. .......           solubility O2 mg/l (100% saturation)
26.0 .........               8.1
30.0 .........               7.5	

The effect of  atmospheric pressure is relevant. At 4,590m (18,000 ft), atmospheric pressure is only 50% of that at mean sea level. For example in Denver, Colorado (at 5,281 ft or 1,609 m), a measured barometric pressure of 760mm Hg would equate to only 626mm Hg at sea level (The atmospheric pressure at this altitude is only 0.83 (83%) of 1 atmosphere)) and at 29oC this gives a 100% oxygen saturation of only 6.34 milligrams O2 per litre. 

So the answer is if you want pearling have cold water, live in Denver, add a lot of CO2.

cheers Darrel


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## Fred Dulley (29 Apr 2010)

ceg4048 said:
			
		

> require high maintenance effort due to higher levels of generated organic waste.



Hi Clive.
Can you give some examples of this organic waste?
Obviously water changes will help dilute this waste but does carbon in the filter help too?
Cheers.

Apologies for going off on a tangent.


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## ceg4048 (30 Apr 2010)

Fred Dulley said:
			
		

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Howdy Fred,
   For starters, here are some examples of general tank organic waste. These are fairly obvious and not all are plant produced:
1. Fish poop.
2. Uneaten food.
3. Dead leaves
4. Dead bacteria

Here are the ones that people never think about:
4. Sugars and other Carbohydrates ejected by the plant.
5. Proteins and lipids ejected by the plant.

Everyone assumes that chemical movement in aquatic plants is unidirectional. That nutrients and water flow into the plant via roots and leaves, but this is only half the story. Plants strip the carbon from CO2 and produce sugar as a fundamental product. Although they use the sugar as their own food, retention is not 100%. These sugars leech across cell membranes into the water column and sediment. This is one way in which they feed the nitrifying bacteria who, many forget, also need carbon for structural building blocks. There is a symbiosis between plant and bacteria. The convert the otherwise inaccessible CO2 to sugar and oxygen and the bacteria use the sugar for fuel, they burn their fuel with oxygen and use the oxygen to detoxify the environment such as oxidizing NH4 to NO3. The "O" in NO3 is Oxygen. So the more Oxygen that is made available, the more NO3 that can be produced, which is then taken back up by the plants.

Plants also leech proteins and lipids which are broken down by the bacteria. The lipids show up as the thin oily film at the surface. In this way, other elements such as Phosoporous, Magnesium and so forth which are needed by the bacteria can be fed to them in an organic form which they can assimilate. So for example, a bacterium does not have access to the Magnesium in MgSO4 but that Mg taken up by the plant is then woven into some organic protein the plant then produces (and later ejects), which the bacterium can later break down and eat, in exactly the same way we access the vitamins and sugars from fruit.

At low levels of light, low dosing and low CO2 these products are ejected slowly (an of course at low concentration levels), but when the environment becomes eutrophic then the ejection rate rapidly increases. In large bodies of water, or in open natural systems the concentrations never become a problem, however, in closed systems such as we have, high rapid organic waste build up is not only fodder for algae as they break down, but they actually stifle plant growth as well, further injuring the system.

In a high tech tank, one of the best things you can do is a water change. The cleaner the tank, the better your plants will grow. This is why the water change is so important in EI. It's ironic that so many people are paranoid about nutrient build up with EI when the real problem is the very products of growth that EI generates as a direct result of the elevated nutrient levels.  

Cheers,


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## Fred Dulley (30 Apr 2010)

Thanks very much, Clive.
Brilliant explanation as always


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