Photoinhibition

Righteous

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Apr 10, 2017
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So I was re-reading Walstad's book and came across the section on photoinhibition. In it she lists that green algae (chlorophyta) are inhibited at 211 PAR.


Has anyone run lights in this range, say 250+ to see what the effect would be? If you could keep co2 stable and high enough and other nutrients available for the plants, would the combination knock the algae out of the running?


Here's more info on photoinhibition. https://en.m.wikipedia.org/wiki/Photoinhibition There are also a number of studies that can be found via google.
 

Tom Barr

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The issue is related more to the specific algae in our aquariums, not just a green alga. Generally speaking, aquatic weeds out compete algae with light. Few have 200 umol of PAR. There's just no need for it. For any plant. As you add more and more light, it causes more and more issues and demand for nutrients, a lot more labor etc.


100 is more than enough.
 

Righteous

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Apr 10, 2017
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I'm by no means advocating running a tank at high PAR. I can certainly see how over the long term, increasing light increases the amount of attention required. Everything is on turbo with high light, so if you slip with nutrients or maintenance, things get out of hand quick.


However, often once some type of algae has taken hold, the advice is to lower the amount of light on the tank. Is it possible that although this is the right long term advice, in the short term dealing with the algae it can be detrimental? It seems like algae is much more efficient at lower light levels than plants. Here's Diana's data:

Code:
Minimum Light Req. (µmol/m2/s)       | Low-Light Growth Efficiency (b)
-----------------------------------------------------------------
      | Median  | Range             | Median  | Range
Algae  |  1.8    |  0.8 - 9          |  7.5    |  0.4 - 44 
------------------------------------------------------------------
Plants |  6.1    |  3 - 12           |  1.1    |  0.2 - 1.8

(b) ‘Low Light Growth Efficiency’ was calculated from the slope (b) of growth versus light intensity.

Walstad, Diana Louise. Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise (Kindle Locations 4903-4911). Echinodorus Pub. Kindle Edition.


So if in an effort to reduce algae, someone, say, sets their lights to 10-20 µmol... could you actually make the problem worse, or at least halt progress? I take it this is also the reason that in order to do a blackout we need to completely cover the tank (algae can get by on tiny amounts of light). So when dealing with algae, making sure we have healthy light levels (at least 40µmol?) is the best course. I know my knee jerk reaction to seeing algae is to lower the light.. but at some point it seems that could be doing more harm than good.


And back to the photoinhibition, might it be possible instead of a blackout to do a "whiteout"... if for three days you could provide perfect CO2 (move livestock to another tank, and crank CO2), maintenance, nutrients, etc but blast the tank with 250µmol... could that put a dent in the algae and give the plants a head start?