Oxygen levels and pearling

[CeeJay]

Hi skeletonw00t

If plants are pearling nicely does this mean that oxygen levels in the water are the highest they can be?

Not neccesarily. There will always be room for more O2 than your plants can produce, but hey, it means you're plants are having a good time

And that co2 levels are ok for shrimp/fish?

No. The more CO2 you add, the faster the plants growth rate and production of oxygen. Therefore you can seriously overdose the CO2 and your plants will look pretty but the tank will be highly toxic to fish and shrimp.
For this reason, when starting a new set up/scape, some people deliberately do not add livestock so they can OD on the CO2 to give the plants the best possible start, and then introduce the livestock after cranking the CO2 back down to levels that are acceptable to the fish and shrimp.
Hope that helps.

 

[dw1305]

Hi all,

Not necessarily. There will always be room for more O2 than your plants can produce"

. This isn't quite right, the pearling really does indicate that the water surrounding the leaves is fully saturated with oxygen, no more can go into solution, so you get a visible bubble of gas. The level of dissolved oxygen will be continually changing dependent upon the availability of light energy and dissolved CO2, the amount of Biochemical Oxygen Demand (BOD, from respiration etc.) and the volume to surface area ratio of the gas exchange surface. If you are adding CO2, a tall, still tank would be much more likely to pearl than a wide shallow one with surface agitation.

However as suggested it doesn't mean that the water in the whole tank is fully saturated with O2, it just means the water in the immediate vicinity of the stomata in the leaf. If you decrease the temperature (O2 is more soluble in cold water) or increase the flow (meaning that the locally oxygen saturated water close to the leaf is replaced by less oxygen rich water), the pearling will stop.

Other factors you have to remember is that oxygen is less soluble than CO2, so it will take longer for the bubble of O2 to dissolve than it would for an equivalent sized bubble of CO2, and that plant architecture makes a difference to pearling, with a dense carpet or fine leaved plant much more likely to pearl than one with a wide flat leaf, as the flow will be impeded by the fine leaves and stems, meaning that it takes longer for the locally produced O2 to be removed.

cheers Darrel

 

[sWozzAres]

I have an Echinodorus Osirus, it produces 2-3 relatively giant glug glug bubbles from it's roots every minute or so. What's that all about?

 

[Fred Dulley]

Oxygen is released by the roots as well. Very handy for nitrifying bacteria in the substrate

 

[CeeJay]

Hi all

I stand corrected . Thanks for the comprehensive explanation Darrel.
I figured the plants would have to go some to saturate the whole water column but some great snippets of information there for the old memory bank.
That's what I love about this place .
Thanks.