# [Wet Thumb Forum]-24 Hour photoperiod for maximum plant growth??



## HighWattage (Feb 11, 2003)

I'm setting up a new tank soon. My objective now is to grow out my plants in the existing tank ASAP. I have a high tech tank with 12 hour photoperiod. I am using EI method of fertilization. I'm getting great result but is curious if I can maximize growth even further by prolonging the photoperiod to maybe 18 to even 20 hours of photoperiod. I like to know if anyone has experimented with such prolonged photoperiod and what kind of results they have seen. I'm sure the law of diminishing return apply to the photoperiod, but at what duration? Would plant grow well given a 24 hour photoperiod?


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## imported_russell (Sep 14, 2004)

i asked this one time in a chatroom, and they told me that plants can only grow so much in one day, and if you lengthened the photoperiod, it would only help the algae out.

i have also noticed that plants can change color and even length at night, so IMO if you were to do a longer photoperiod, it might even hurt the plants by not letting them do their normal cycle.


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## Bert H (Mar 2, 2004)

Nature has cycles of light and dark. On my tanks the photoperiod is 10 hours, (on at 1PM, off at 11PM). Around (9:30-10:00PM, you can actually see some of the plants start to go into a 'sleep mode', as I call it. On my Rotala, and Limnophila for example, the whorl of leaves will actually close up, much like a flower would. 

When I first started with planted tanks, I tried 12-14 hours of lights. It got me more algae issues than anything else. IMHO, more than 12 hours is just an invitation for algae to come and take a hold.


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## John N. (Dec 11, 2005)

I agree with Russell and Bert. You'll run into algae issues which hurts your plants in the long run. Plants do need a "sleep" cycle to complete their respiration of O2 and CO2. They bring nutrients, and create storage units within the leaves and stems at night, as the nutrients are no flowing up and down the stem. It gets more technical than that but for simplicity, its better to stick to a normal cycle. 

Since it's a high tech tank, your plants will grow out quickly before you know it. Just keep your lights on 10-12 hrs, inject co2 and light and you'll be trimming in less than 3 weeks. 

John N.


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## Jason Baliban (Feb 21, 2005)

Plants need the dark period or Calvin cycle to make food. Without it, they will actaully die.

Light-Independent Reactions (dark reaction/calvin cycle)

* Calvin Cycle
o Carbon dioxide combined with RuBP and then combined molecules are converted to sugars (Glucose).
+ Energy furnished by ATP and NADPH from Light-Dependent Reactions.

Light Independent Reactions - In Depth

* Calvin Cycle
o Six molecules of CO2 combine with six molecules of RuBP with the aid of rubisco.
o Resulting complexes split into twelve 3PGA molecules.
o NADPH and ATP supply energy and electrons that reduce 3PGA to 12 GA3P.
o Ten of the twelve GA3P molecules are restructured into six RuBP molecules

Here is the link to the whole article if you are interested.

http://academic.kellogg.edu/herbrandsonc/bio111/metabolism.htm

jB


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## HighWattage (Feb 11, 2003)

I am aware of the calvin cycle. My question really concern the optimal photoperiod for a high tech tank. I'm curious if anyone actually experimented with different photoperiod while holding all other variables constant. 

The general consensus seems to be 12 hour of dark and 12 hour of light period. But, is this proven scientically? My hypothesis is that maybe 14-16 hours of photoperiod might induce the most plant growth. Who knows? Maybe 8 hours is enough for a high tech tank and 14+ hour for a low tech tank. I'm just guessing here. I'll run a test this month and see what happens. 

Another thing, I left the light on in my tank for over 24 hours yesterday and the plants are still pearling like crazy.


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## Jason Baliban (Feb 21, 2005)

I only run my tank for 8 hours.....

I can see the plants closing up even before that.

jB


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