# Split Photoperiod



## Worshiper (22 Apr 2014)

Sorry if this is a repost. I couldn't find it in the search option.

I wanted to know if I can split the photoperiod as follows:

7am to 11am (lights on)
11am to 5pm (lights off)
5pm to 10pm (light on)

This is only because I like the lights on before I leave for work in the morning and when I get back from work.
I use diy co2 and ei dose.

Will this affect the plants negatively? 
Also, do I have to ei dose before the lights are switched on?

Many thanks guys!


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## Tim Harrison (22 Apr 2014)

In the low-energy world this is called a siesta period. It allows CO2 levels depleted by photosynthesis to build up again, supposedly benefiting plant growth and reducing algae
There is no conclusive quantitative evidence as to its efficacy, but I use a siesta period in my low-energy tank and I've noticed an improvement in plant health, if not growth, and a reduction in algae...that is opposed to not using one, which I have also experimented with.
So I don't see why it wouldn't work for you, especially given that you are using DIY CO2, and I definitely don't think it will do any harm. But it's a contentious issue and your question might spark an interesting discussion

Edit: although there is always the caveat of - don't gas your fish and critters


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## Humbert (22 Apr 2014)

In my experience (also checked with other people), the pause in the photoperiod is neither beneficial nor detrimental for the plants and/or algae.
It is however important that the minimum continuous photoperiod is at leas 4 hrs, otherwise plants do not have enough time to photosynthetise properly.

I also like to have the lights on in the morning before going to work, which is why my lights are on for 1/2 hrs in the morning and 8 hrs continuous starting 14:00.
Wouldn't that sort of schedule work for you as well?


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## Nathaniel Whiteside (22 Apr 2014)

I recently tried a 'siesta' period of 1.30 in a 6 hour photoperiod. 

I found after about a week, my tank was covered in green and brown algae on the surface of both hardscape and glass.
I think the plants may find it hard to shut down and start photosynthesising again in such a short period. 

It's not conclusive, and wasn't 'variable free' but It was done as a specific test and definitely put me off ever considering one in future.


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## Worshiper (22 Apr 2014)

Yeah.  I dont think there was any conclusive evidence of it reducing algae. Although some claim it helped them. May be like a placebo effect.
My purpose was jus for viewing pleasure when I wake and get back from a hard day's work. Thats the purpose of a planted aquarium.
I still have to master the art of maintaining it though.
Thanks for the responses. Hope this sparks up a good conversation because the last I read about split photoperiods was ages ago!


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## Sacha (22 Apr 2014)

A siesta is a very bad idea. 

Please see this post (from Clive): 

CO2 is THE most important ingredient for making the sugar. Without CO2, shining a light on a plant is about as effective as boiling it in a soup. Plants produce what is probably the single most important enzyme called Ribulose-1,5-bisphosphate carboxylase oxygenase, normally abbreviated to "RuBisCO". All carbohydrates on the planet are made possible by the action of this very complicated enzyme. Here is a typical image:

The areas in dark grey and light grey are the areas on the enzyme where individual CO2 molecules are attracted and held. They are then transported to an area where the Carbon portion of CO2 is combined with other molecules to create a form of glucose.

Despite its huge importance in life, RuBisCO is, by enzyme standards, rather slow, with a turnover rate of between 3 and 10 CO2 molecules per second. Typical enzyme reaction rates are somewhere around 1/2 million molecules per second. So the first two severe limitations to this enzyme are:
1. Complicated and energy expensive molecule for a plant to manufacture, which may require a few weeks to adjust the levels.
2. Very slow reaction rate.

The central role of RuBisCO in the process of photosynthesis means that it must be tightly regulated, to ensure that it is active only where and when it should be. One important layer of this regulation is the activation of RuBisCO at the beginning of the day. During the night, the RuBisCO active sites are blocked by inhibitors. So, at the beginning of the photoperiod, the plant then has to re-activate the binding sites by removing the inhibitors from the CO2 binding sites. This means that there is another set of proteins which are sensitive to light. There are additional regulators to ensure that RuBisCO only operates at daytime. Magnesium typically increases as the chlorophyl molecules become active so the sensors monitor the movement of Mg++. So here is a third limitation:
3. Activation of the enzyme is very slow at the beginning of the photoperiod. The RuBisCO in algae is more efficient because algae have a mechanism which concentrates CO2 and holds it, so they respond very quickly to the daylight. This is why siestas are a very bad idea.


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## Sacha (22 Apr 2014)

Source here 

http://ukaps.org/forum/threads/ei-calculators.26669/


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## Tim Harrison (23 Apr 2014)

I'm not so sure it's that simple. In a low energy tank light levels are traditionally relatively low anyway, and in the case of my tank there is probably enough ambient daylight to maintain photosynthesis during the siesta period - especially since it has an open top - all be it at a slower rate and perhaps somewhere around the compensation point. To paraphrase Diana Walstad, switching the lights off mid-photoperiod is analogous to temporary clouding during a summer afternoon.

So it's not necessarily a costly stop-start process, and especially for a tank with CO2. Higher levels of CO2 increase the light use efficiency. Although, of course, a siesta period is totally unnecessary in a fuel injected tank, it's obviously desirable in the context of the OP. 

So in the case of low-energy tank, at least, I guess the theory assumes that during the siesta period there is enough ambient light to give plants the long daylength they require, and also to allow CO2 regeneration, so when the light comes back on plants can photosynthesise more effectively. 

With regards the inhibition of algae, again in a low-energy tank, I suppose the theory is based on the supposition that algae is more efficient at taking up CO2, as Clive's piece intimates. Therefore, algae gains an advantage over higher plants when CO2 concentration drops during the afternoon. Once again, the siesta period supposedly redresses this problem by allowing CO2 regeneration. 

_Sources: Diana Walstad: Ecology of the Planted Aquarium, 2nd ed, p179_. and http://www.tropica.com/en/tropica-abc/basic-knowledge/co2-and-light.aspx


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