# Two Light Cycles In 24 Hours?



## Teebo (Jul 15, 2015)

I have seen people use dual light cycles breaking up the light to prevent algae blooms, such as 4 hours in the morning and 4 hours in the evening. I thought that was nice so I can have a lighted tank when I wake up then again before I fall asleep (the tank is in my bedroom). For me this would be 9am-1pm then 10pm-2am but I am thinking this may cause issues for the plants mostly flowering plants, because it is very un-natural to have such a late light cycle from 10pm-2am even though they will have a dark period from 2pm-9pm they will get minor window sunlight, then have a 7-8 hour blackout between 2am and 10am. I do have water lilies which open and close based on light, as well as other emerging flowering plants. 

What is your thoughts on running my dual 4 hour lighting cycle?


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## TankPlanter (May 31, 2015)

Bump! I'm running 4h on, 3h off, 5h on. I'm not sure if it's working, as plant growth is not going great, so I'm interested in the same question.


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## Steve001 (Feb 26, 2011)

For no reason other than to accommodate a schedule I've not read of a reasonable reason to do this. It's probably not good for plants in the long run.


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## Teebo (Jul 15, 2015)

Im thinking the same thing, it has been raining for 2 days after being dry and its been cloudy for 2 days including today so I went to the pond and to my surprise all the lily's are open so Im not sure if light is always a trigger I wonder if the rain made them open.


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## Audionut (Apr 24, 2015)

In a low tech tank, when the lights are off, CO2 levels increase.

So the idea being, when the light comes back on for the second photoperiod, the CO2 levels have risen during the dark period.


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## Diana (Jan 14, 2010)

I have also seen the idea as a way to slow the growth of algae. In theory the plants can 'wake up' faster than the algae, so when the light comes on the plants get a jump start on using the increased CO2 that has built up through the dark period. 

Having 2 dark/light periods gives the plants 2 such boosts.


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## Seattle_Aquarist (Jun 15, 2008)

Teebo said:


> I have seen people use dual light cycles breaking up the light to prevent algae blooms, such as 4 hours in the morning and 4 hours in the evening. I thought that was nice so I can have a lighted tank when I wake up then again before I fall asleep (the tank is in my bedroom). For me this would be 9am-1pm then 10pm-2am but I am thinking this may cause issues for the plants mostly flowering plants, because it is very un-natural to have such a late light cycle from 10pm-2am even though they will have a dark period from 2pm-9pm they will get minor window sunlight, then have a 7-8 hour blackout between 2am and 10am. I do have water lilies which open and close based on light, as well as other emerging flowering plants.
> 
> What is your thoughts on running my dual 4 hour lighting cycle?


Hi Teebo,

I have done split photoperiods for over 7 years now and my plant growth is fine. Typically I have my lights on 8:00 - 10:00 AM and 7:00 - 10:00 PM. My plants are healthy and growth is very good.


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## Teebo (Jul 15, 2015)

Audionut said:


> In a low tech tank, when the lights are off, CO2 levels increase.
> 
> So the idea being, when the light comes back on for the second photoperiod, the CO2 levels have risen during the dark period.


Are you referring to people who run un-timed CO2 systems? 



Diana said:


> I have also seen the idea as a way to slow the growth of algae. In theory the plants can 'wake up' faster than the algae, so when the light comes on the plants get a jump start on using the increased CO2 that has built up through the dark period.
> 
> Having 2 dark/light periods gives the plants 2 such boosts.


That is new to me!



Seattle_Aquarist said:


> Hi Teebo,
> 
> I have done split photoperiods for over 7 years now and my plant growth is fine. Typically I have my lights on 8:00 - 10:00 AM and 7:00 - 10:00 PM. My plants are healthy and growth is very good.


Thanks! Any flowering plants?


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## Audionut (Apr 24, 2015)

Teebo said:


> Are you referring to people who run un-timed CO2 systems?


No CO2 injection. 

With CO2 injection you can control CO2 levels directly.


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## Teebo (Jul 15, 2015)

Audionut said:


> No CO2 injection.
> 
> With CO2 injection you can control CO2 levels directly.


Not pumping any more in is one thing, but if it builds up without it then you can not really control the levels with injection only add to it...


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## Audionut (Apr 24, 2015)

The CO2 level in an aquarium is always trying to reach equilibrium with the atmosphere. Since injection is increasing the CO2 concentration above equilibrium with the atmosphere, the water is constantly off gassing CO2 to reach equilibrium.

So while your statement is true, in practice, as soon as you stop injecting CO2 into the aquarium, CO2 levels drop to reach equilibrium with the atmosphere.

Where you manually control CO2 injection (no pH controller), and target a specific pH, you're actually maintaining CO2 injection at equilibrium with water off gassing, at that specific pH. ie: You're injecting just enough CO2 to cover the off gassing.

In a tank without injection, the reverse almost comes true. Here, plants consume CO2 during the photoperiod, reducing the CO2 concentration below equilibrium with the atmosphere, and hence with lights off the tank is increasing CO2 concentration from the atmosphere to maintain equilibrium. Thus the dual photoperiod. Turn the lights off in the middle of the photoperiod to allow CO2 concentration in the water to rise.


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## TankPlanter (May 31, 2015)

I'm running a very low tech, no CO2 tank, and wondering about the "siesta" period (whenever I've googled it, I just see lots of debate. Walstad pro, Barr con...) I think I'm going to try it both ways and see how it affects my particular (struggling) system. If OP has a high light, CO2 added tank, that's a different gig... As the algae and CO2 rationales change. Would love to know if any low techs have actually tested it, but that might not be OP's Q.


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## Diana (Jan 14, 2010)

I ran a siesta period for a few years. Not for algae, but to keep the temperature a bit cooler through the summer. On for several hours in the AM, off for 2-4 hours in the heat of the day, on for several more hours in the evening. Many of these tanks were in rooms with a window, but I had sheer curtains to cut out some of the light (and heat). Ambiant light was not enough to trigger pearling. I occasionally saw pearling when the direct sun hit the tank. 

Low tech tanks, some dosing, but mostly K and Fe. Fairly high stocking levels, so fish food was the main source of nutrients. I also tried DIY/yeast CO2, but I do not remember how that tied in with my trials with the siesta timing. 

The first year I did notice less algae. 
Then I went back to regular lighting through the winter, no mid day break. 
The next year I did not notice much difference in the algae.


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## Teebo (Jul 15, 2015)

I have both high and low tech tanks I wanted an answer for 

Mainly I would do it for viewing schedule reasons; my own personal enjoyment for my bedroom tanks. I may try it and if there are no problems I will roll with it, they will get an 8 hour dark period but with morning sunlight through blinds before 10am...could simulate the moon may not be a bad thing.


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## BigJay180 (Jul 20, 2014)

Pros: (most mentioned above)
* Algae takes a longer photo-period to grow.
* CO2 builds up between photo periods for low tech tanks.
* You can enjoy your tank before work and when you get home.
* The fish don't care. No, they really don't.

Cons:
* The only CON I've read from Barr is that multiple stop/starts wear out the bulb faster for fluorescent fixtures.

http://www.barrreport.com/forum/bar...pics/4901-split-photo-period-siesta-pros-cons

This isn't a problem if you're already replacing the bulbs annually.
* Slower growth? Low tech is always slow, I don't see it as an issue.


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## Steve001 (Feb 26, 2011)

Diana said:


> I ran a siesta period for a few years. Not for algae, but to keep the temperature a bit cooler through the summer. On for several hours in the AM, off for 2-4 hours in the heat of the day, on for several more hours in the evening. Many of these tanks were in rooms with a window, but I had sheer curtains to cut out some of the light (and heat). Ambiant light was not enough to trigger pearling. I occasionally saw pearling when the direct sun hit the tank.
> 
> Low tech tanks, some dosing, but mostly K and Fe. Fairly high stocking levels, so fish food was the main source of nutrients. I also tried DIY/yeast CO2, but I do not remember how that tied in with my trials with the siesta timing.
> 
> ...


You probably had some photosynthesis occurring with window light. 
When I first joined this forum I remember thread that tested minimum levels at micromols that photosynthesis could happen. I was surprised at how low those levels were. I think the minimums were down to 3-4 mmols. I should have bookmarked it.


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## Steve001 (Feb 26, 2011)

BigJay180 said:


> Pros: (most mentioned above)
> * Algae takes a longer photo-period to grow.


This might not be true. Algae being a single cell undifferentiated plants only need to divide one cell to produce two cell then divide again to produce four new cells... Vascular plants have to create new specialized cells while they grow.


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## klibs (May 1, 2014)

I have tried dual photoperiods some time ago and am not a fan. IME lowering light levels and maintaining a 7-8hr photoperiod is more effective at solving algae issues. I am also a believer that plants need at least like 3-4 hours to 'get going' and really start to grow. Not sure about the science behind that but I get much better growth without a break in my photoperiod.


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## Teebo (Jul 15, 2015)

BigJay180 said:


> Cons:
> * The only CON I've read from Barr is that multiple stop/starts wear out the bulb faster for fluorescent fixtures.


Thats alright I run all LEDs and they work fantastic!


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