# Photosynthesis times?



## Ian Holdich (30 Sep 2011)

I remember reading somewhere about plants reaching there maximum intake of nutrients around the times of 4-6hours after the lights come on. After this they start to decrease the intake and eventually shut up shop. I'm sure it was on the Barr report somewhere... 

I know that this will vary under different lighting conditions/fert regimens, but i'm sure it was based on an average.

was i dreaming this or did i really read that somewhere?


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## Alastair (30 Sep 2011)

Your right I've read it on here somewhere. I think Clive mentioned it when talking about co2 needing to be as spot on as possible during the first few hours of lighting as this is when plants need it most, and by the evening they take a bit of a back seat as they've had there fix lol


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## Ian Holdich (30 Sep 2011)

I thought i'd read it somewhere! lol

does anyone have a link to the discussion or the evidence backing these statements up?


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## Alastair (30 Sep 2011)

Good luck finding it ha ha. I'll have a look through to see if I can spot it but doubt I'll find it


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## Ian Holdich (30 Sep 2011)

cheers Alastair, i can't find it anywhere!


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## Alastair (30 Sep 2011)

If you can't find it either mate give Clive a pm and he will explain it all to you.


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## ceg4048 (1 Oct 2011)

Hi Ian,
            One has to be careful to use the proper words so as not to muddy the waters with different principles which, lthough related, are distinct. Barr noted that submersed macrophyes typically have a photoperiod of about 8-9 hours, after which food production activities decline. These limits don't seem to apply to algae so that long photoperiods tend to encourage algal blooms while having marginal benefits to plants. The expression "maximum uptake" is more accurately associated with the rate of uptake and of food production. The uptake rate will depend on nutrient/CO2 availability during the photoperiod.

The need to optimize CO2 at the beginning of the photoperiod has more to do with the food prodution inefficiencies at lights on due to the thousands of individual photosynthetic reactions. In other words, the engine s just getting warmed up inthe early part of the period. Fixing  Carbon is a top priority, so it has to be available otherwise the system is more vulnerable to shortfalls. That's the reason for the 2 hour gas initiation prior to lights on. It's because of our inability to provide good distribution and saturation that we need to do this. 

By the 6 hour mark the plants have fixed plenty of carbon and the injection has saturated the water as well as the fact that the system is starting to shut down, so there is much less emphasis on the gas availability by then. That's why we can shut the gas off early without ill effects. A lot of our CO2 problems actually are occurring in the early part of the photoperiod.

Cheers,


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## Ian Holdich (1 Oct 2011)

thank you Clive...thats cleared that up for me.


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## plantbrain (2 Oct 2011)

Seems most important to get plenty of growth when the first 1-2 hours of the day cycle IME via good CO2.

After this, it seems things are more forgiving.

Other things like less light intensity, lots of algae eaters, eg Amano shrimps etc............decent flow on and on.


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## Gary Nelson (3 Oct 2011)

Is it better to have a break in between lighting times, say a 2-3hour break half way through? or just have the lights on 7-8hours straight?


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## ceg4048 (4 Oct 2011)

Hi,
    The 2-3 hour break serves no purpose. That will be 2-3 hours of lost food production for plants. It's more useful to avoid excessive intensities or to avoid poor CO2/flow than to stop production of vital energy reserves.

Cheers,


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## ghostsword (4 Oct 2011)

I just have my lights for 6 hours, no burst, just plain 80w on a 120l tank, the co2 comes on 3 hours before lights on and stops an hour before lights off. 

My plants grow nicely, even blixa that is under some echinodorus grows very thick and bushy.

I could add more light, as the Arcadia has another set of lights to use, but I do not see a need for it.

Got some bba at the back on the wood, too many plants restricting the flow, but does not bother me, nothing on plants.

I have found that less is more when dealing with lights. I have not done a iwagumi with hc or glosso, so maybe with those would be different. 


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