# photo period confusion



## mommyeireanne (Oct 24, 2007)

Well I always heard to have a night/lights-out for planted tanks, but of course that was for rooted plants in soil tanks. I get that a plant is alive and performing it's functions even in the dark, so I believed (and shared) the advise to have a dark time. If this supposition is not correct, what is the scientific evidence? Is down time just about the water CO2 level? And fish comfort? 
*What then is the ideal photo period for a rooted-plant NPT with fish inhabitants*? Keeping in mind algae and any other important factors.


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## NeonFlux (May 15, 2008)

7 hours


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## cs_gardener (Apr 28, 2006)

For a NPT, Diana Walstad has recommended a 12 hr photoperiod although including a mid-day "siesta" period of 2-3 hrs is okay. As further experimentation is done I'm sure the recommendation will change (or maybe it already has). I've had good luck with the long day and a mid-day break. My tanks never get really dark during the mid-day "siesta" because of ambient lighting.


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## dwalstad (Apr 14, 2006)

mommyeireanne said:


> Well I always heard to have a night/lights-out for planted tanks, but of course that was for rooted plants in soil tanks. I get that a plant is alive and performing it's functions even in the dark, so I believed (and shared) the advise to have a dark time. If this supposition is not correct, what is the scientific evidence? Is down time just about the water CO2 level? And fish comfort?
> *What then is the ideal photo period for a rooted-plant NPT with fish inhabitants*? Keeping in mind algae and any other important factors.


Not to worry.

The scientific evidence that I have recently found shows that several aquatic plants will grow much better with a longer photoperiod (that is, 22 hr and/or continuous light). This information is very useful for those setting up refugiums (water purification systems using aquatic plants) and those that grow aquatic plants to sell.

For ordinary situations and NPTS, I would follow what CS-Gardener recommends. My own tanks run with a 14 hr day and a 4 hr siesta. Works great!


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## HeyPK (Jan 23, 2004)

I know of one or two exceptions to the claim that 24 hours of light is good for aquatic plants. _Hygrophila polysperma_ and some other Hygrophilas on 24 hours light produce distorted leaves with no air filled spongy parenchyma between upper and lower epidermis. The leaf looks narrower, distorted and dark green because of the lack of any air in the leaf. Back in the days when _H. polysperma_ was not on the Federal banned list I could always tell if a pet store kept their tank lights on for 24 hours by looking at the leaves on the Hygrophila. Also, the alga, _Hydrodictyon_, water net, can't form its nets with their six sided openings in 24 hours light apparently because mitosis is limited to the dark period. According to a paper I ran across, there are a number of algae, including _Cladophora_, that only do mitosis in the dark. I wonder if the absence of a dark period could kill _Cladophora_, if you kept it up long enough.


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## davemonkey (Mar 29, 2008)

Lighting seems to be one of those things that 'just depends'. Light intensity, fertilization, Natural methods vs. high-tech, etc...

I read about dwalstad's split photoperiod once and tried it (14 hrs with a 4 hr rest) . I have to say I am very pleased with the results and I wouldn't change it. But I also know those who light for 7 hours, or 8, or 9, or 10...and everyone of them has great growth and healthy plants.

Very interesting info about continuous light and hygro and the alga. I have a 1 gallon "experiment station" at work on my desk. I think I'll try that with some mosses and plants and see what I end up with. I'll update if anything cool happens. 

-Dave


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## dwalstad (Apr 14, 2006)

HeyPK said:


> I know of one or two exceptions to the claim that 24 hours of light is good for aquatic plants. _Hygrophila polysperma_ and some other Hygrophilas on 24 hours light produce distorted leaves with no air filled spongy parenchyma between upper and lower epidermis. The leaf looks narrower, distorted and dark green because of the lack of any air in the leaf. Back in the days when _H. polysperma_ was not on the Federal banned list I could always tell if a pet store kept their tank lights on for 24 hours by looking at the leaves on the Hygrophila. Also, the alga, _Hydrodictyon_, water net, can't form its nets with their six sided openings in 24 hours light apparently because mitosis is limited to the dark period. According to a paper I ran across, there are a number of algae, including _Cladophora_, that only do mitosis in the dark. I wonder if the absence of a dark period could kill _Cladophora_, if you kept it up long enough.


Now this is interesting!  Thanks for the input.

There does seem to be an interesting bio-rhythm to algae. In addition to what you've written, the marine alga _Gonyaulax polyedra_ bioluminesces in the dark, photosynthesizes in the day, and divides in the dark just before dawn. My textbook* goes on to say, "If Gonyaulax is kept in continuous light, these three functions continue to occur with the same rhythm for days and even weeks, long after a number of cell divisions have taken place."

As to aquatic plants, I would agree that some species may look different with continuous light, but that doesn't mean that they've decreased their productivity. If you can find a paper that compares growth rates/biomass production of aquatic plants that shows decreased growth with continuous light, I'd love to see it. So far, all I've found is either no change or a major (and statistically significant) increase.

*Raven PH, Evert RF, and Eichhorn SE. 1992. Biology of Plants (5th Ed.), Worth Publishers (NY), p. 578.


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## mommyeireanne (Oct 24, 2007)

I have heard of lots of different time frames also. I have been doing a 14 hr period with an afternoon break of 2-3 hrs for a while and they seems to help keep the BBA at bay. (unless I forget to do the lights out afternoon.) Thank you everyone. I want to give the plants what they need.:thumbsup:


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## Sarge (Dec 13, 2008)

I was sent here from TPT forums (plantedtank.net) to get dwalstads' advice or input on something similar to this discussion, but instead of too much or long photo times, my interest is in the dark times.

Allow me to explain my thoughts. Outside nature is governed by itself on a 24 hour schedule, albeit sometimes changing, but nature has its' best benefit in mind I believe. In our aquariums, we are the governers, and decide what is best. (Or worst for the first few days I started planting my tanks )

If light is what encourages growth, tells our plants to start sucking up nutrients. At night they respire, and reach for the skies. (but I'm a soldier and value my sleep time) 

What is the minimum downtime for plants? IS it possible and still healthy for a 9 hour on, 9 hour off cycle?

Quote from Naja when asked the same ? on TPT:

"Ok, it's sounds like you are wondering if we can "add more days to the year" by using a minimum dark cycle. I've pondered that--6 hrs On, 6hrs Off x2/day, etc. I don't know the answer, but I've pondered the thought."

Thank you for your time


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## HeyPK (Jan 23, 2004)

I suppose you could give plants 'days' that are longer or shorter than 24 hours. One thing I know is that the photoperiod---the part of the day that plants measure and which determines whether they flower or grow vegetatively or go dormant---is the dark period. Long day plants are really short night plants that require a night shorter than some length of time in order to bloom. Short day plants are really long night plants that require a night longer than some amount of time in order to bloom.


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## Sarge (Dec 13, 2008)

HeyPK said:


> Long day plants are really short night plants that require a night shorter than some length of time in order to bloom. Short day plants are really long night plants that require a night longer than some amount of time in order to bloom.


Can you please give some examples as to wich plants you are referring to?

Ok so with the period of their 24hour cycle (outside of aquaria), plants decide how they grow at night?

During the day they soak up nutrients, and store them as food once broken down into something they can actually use. So I assume that it's safe to say, the growth rate is dependent upon the amount of nutrients stored readily as food, wich is dependent upon the light intensity, dependent upon the length of lighting time. Once lights are out, the plants grow in relation to amount of food stored? What is the ratio, term, length, timing of lights out time, when the plant says "Hey, look buddy, I just can't grow no more, show me the liiiiiiiiiiiiiiiiiiiight!"

Correct me if I'm wrong please.


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## HeyPK (Jan 23, 2004)

> Can you please give some examples as to wich plants you are referring to?


Christmas cactus is a long night plant. It won't bloom unless it has a long, uninterrupted night. Some Echinodorus species bloom only with a short night and some bloom only with a long night. In general, tropical species near the equator are not sensitive to night length, but temperate species are. If temperate species bloom in late spring or summer, they are short night plants, and, if they bloom in the fall, they are long night plants.



> During the day they soak up nutrients, and store them as food once broken down into something they can actually use. So I assume that it's safe to say, the growth rate is dependent upon the amount of nutrients stored readily as food, wich is dependent upon the light intensity, dependent upon the length of lighting time. Once lights are out, the plants grow in relation to amount of food stored? What is the ratio, term, length, timing of lights out time, when the plant says "Hey, look buddy, I just can't grow no more, show me the liiiiiiiiiiiiiiiiiiiight!"


I am pretty sure that most plants grow both when the light is on and when it is off. There are exceptions, as in some of the algae mentioned previously where they limit cell divisions to the dark period. It is also safe to assume that plants will grow more given longer days than shorter days at the same light intensity.


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## dwalstad (Apr 14, 2006)

Sarge said:


> Once lights are out, the plants grow in relation to amount of food stored?


Yes.


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