# What photoperiod do our plants really need ?



## tubamanandy

I've done alot of reading about the photoperiod our plants need but I'm no wiser.

Can someone clarify what photoperiod our plants need ? I get the feeling that 7-8 hours is simply not required and at least 2-3 hours of this is for our benefit only.

What works well for most of you ?


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## sa80mark

Im not experienced enough to give a solid answer but for me 6 hours has worked well and ive had no desire to increase this


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## Victor

The correct is 8 to 10 hours. Begin with 8 hours and increase the photoperiod slowly until you target 10 hours.


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## greenink

Six to seven


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## Michael W

I use 5 hours for my 2 nanos and 6 for my others. 5 hours is working very well for my Nanos, I am growing things like dwarf sag, rotala, ludwigia repens and staurogyne repens (which I failed in the same tank with longer photo period months and months ago) and java fern, Echinodorus Vesuvious, mircoswords, anubias and fissidens fonantus. 

Sure growth is slow for *some of the* *plants*  but overall they are healthy and the tanks have little algae which is neglectable for me as I have shrimps which loves to graze on it.


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## darren636

Mine are on four hours.


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## tim

I use 6-8 hours depending on lighting t8s 8 hours is fine IMO t5 shorter photoperiod is plenty.


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## Nathaniel Whiteside

So, to summarise, there is no hard and fast answer.

Depends on your setup, how quickly you want your plants to grow, how much money you have to get gas refills & nutrients, how much time you desire to spend on maintenance, how much you want to pay for electricity.

You could light 24/7 if you really wanted to, as plants apparently do not require any break in photoperiod. Obviously if they're is livestock in the tank, they do require a 'rest' from light.

I would tend to go around a 6-7 hour period, never more than 8.


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## dw1305

Hi all,
It depends on the plant, but most terrestrial plants grow fastest on a 16 -18 hour day <GROWING GREENHOUSE TOMATO AND SWEET PEPPER UNDER SUPPLEMENTAL LIGHTING: OPTIMAL PHOTOPERIOD, NEGATIVE EFFECTS OF LONG PHOTOPERIOD AND THEIR CAUSES>, and a lot of quick growing salad crops etc are grown under 24 hour daylight, although not all crops can be grown without a dark period long-term <Plant Circadian Rhythms >.

Some-one may know definitively, but my suspicion would be that "Tropica" etc use a 16 hour day (or possibly even longer) for their emersed plant production. The future for commercial horticulture will be:





> ".... been developing a biofeedback system in which the physiology of the plant regulates the spectrum and intensity of LED arrays <Plant Physiology Expert Joins Lighting Research Center at Rensselaer | News & Events>"


 If you think about the natural habitat for most of our plants you are going to be talking about somewhere near the equator, so a 12 hour day is probably what they are adapted to. I always have a 12 hour light period, and the tanks get quite a lot of ambient light. I just have plant mass in the summer and all my tanks are low tech.

With high light intensity, EI and CO2 addition things are obviously slightly different, in that the plant won't be limited by nutrient availability (including CO2) and you can tell that photosynthesise is occurring rapidly by the pearling from O2 production. There is obviously a limit to how long this can go on, and I'm not a plant physiologist, but Clive wrote:





ceg4048 said:


> Photoinhibition occurs all the time, regardless of light intensity, because it is a function of the number of photon hits the chloroplast absorbs. The photosynthetic reaction centres of the chloroplasts have the capability to repair the damage, but when the light intensity is too high, then essentially, the rate of damage to the photosystems exceeds the rate of repair. This leads inevitably to a reduction in food production via an inability to use the CO2 that you are injecting because of this damage rate.


 <Woah green algae! | Page 2 | UK Aquatic Plant Society> & <Enough Light? | UK Aquatic Plant Society> and I suspect that is what is happening with a longer photo-period.

cheers Darrel


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## Michael W

Hi Darrel, I'm quite intrigued about you having 12 hours photoperiod. I understand that you use a lot of floating plants and other plants like water sprite in your tank, I'm guessing because of the heavy plant mass, you can get away without much algae? Because my thinking has been the increased photoperiod  of 12 hours with a low light will = a very high power light that is say on for 7 hours which can wrech a low tech tank or am I wrong? 

Michael


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## dw1305

Hi all, 





Michael W said:


> I'm quite intrigued about you having 12 hours photoperiod. I understand that you use a lot of floating plants and other plants like water sprite in your tank, I'm guessing because of the heavy plant mass, you can get away without much algae?


 I suppose so, I just let the plant mass grow, and then I ignore it other than fishing out any dead leaves. I thin the floaters out more regularly in the winter. In most of the tanks I've got plenty of bits of wood, spare plants etc in storage, so there is no open water or free swimming space, as such at all. In this one you can see there is a bit of green algae on the older leaves, but I can't see many snails in that one (it is from 2009 ish). This is the tank in my kitchen, and I still have the all of the same plants in it (many of them the same plants in the same places).





This is the tank at the back of the lab. Both tanks get a lot of ambient light from windows.












In the past I've had 400W SonT grow lights over tanks in the glasshouse with diluted landfill leachate in them, and they initially grew some green filamentous algae, but once the plant mass filled out they were fine.

cheers Darrel


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## Michael W

Thanks for the information explanation Darrel. Lovely Apistogrammas and checkerboard cichlids! I'm a big fan of them myself, its a shame that my A. Hongsloi recently passed away after quite some years, he looked pretty old when I got him, they're quite long lived.


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## critch

This was grown purely by natural light, got silly at one point,

Light above it was purely to take the photo

Sent from my ST25i using Tapatalk 2


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## dw1305

Hi all, 





Michael W said:


> checkerboard cichlids!


 They were lovely, but I subsequently managed to kill them off, details here <1st  D. maculatus spawn | Apistogramma.com>.  I haven't got any _Apistogramma_'s either at the moment, although I will start again with another species, possibly _A. baenschi._

cheers Darrel


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## roadmaster

Darrel,
Your tank's resemble my own, love em.
Imagine photo of my avatar tank 300 litre, with four or five inch deep matted cover of water sprite.
Some fishes I have not seen in month's .
Is my understanding that in low tech,where only naturally produced CO2 is available,,that plant's use this up within an hour or two after light's on for the day.(Might have been Tom who suggested this).
Don't see any benefit to photoperiod longer than eight hour's for these tank's??
I do have a smaller 55 gal with one 32 watt T8 that get's ten hour's.some suggested that the single 32 watt bulb would not grow much of anything but...someone forgot to tell the plant's that.
Water sprite,anubia,pennywort,anacharis,vallisneria, all do well but VERY slowly which suit's me for now.


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## dw1305

Hi all, 





roadmaster said:


> with four or five inch deep matted cover of water sprite. Some fishes I have not seen in month's .


 Know what you mean, I was contemplating thinning the Water Sprite this morning, I think our version of jungle and "heavily planted" are probably a bit different from the average. I'd really like Edvet's triffid (_Ceratopteris pteroides_ (from <Restarting 400 gallon | UK Aquatic Plant Society>)) you can imagine it fighting back when you tried to remove it.





roadmaster said:


> Some fishes I have not seen in month's .


 When I say to people that I didn't know I had _Corydoras hastatus _left, and that I hadn't seen them for months, but when I had to move the tank I found they'd spawned and I had considerably more than I started with, I think they think I'm either lying, deluded or very short sighted.





roadmaster said:


> Is my understanding that in low tech,where only naturally produced CO2 is available,,that plant's use this up within an hour or two after light's on for the day.


The CO2 will definitely be depleted, but there will be more diffusing in all the time, it is going to depend upon tank architecture and water turn-over. If the tank has very low dissolved CO2 levels the concentration gradient between atmospheric and dissolved CO2 is going to be fairly steep, so this is going to act as negative feedback, depleted CO2 = quicker diffusion. I think one reason "Alastair's" and "BigTom's" tanks are so amazing is their large surface area to volume ratios.

If you really wanted to work out what was happening you would need a pH probe and some measure of dKH in the water. You could then measure pH every 15 minutes or so through the photo-period, the rise in pH should give you a pretty good idea of how far the CO2 has been depleted. The rising pH will actually be indicating the degree of oxygen saturation, but CO2 level will be near enough the value given by the dKH/CO2/carbonate relationship.

I've never done it systematically, but when I have dipped the pH meter in before lights on, we've usually been somewhere around pH6.5, and mid afternoon (so well into the photo-period) about pH8. I've also played with the Dissolved Oxygen meter at the same time, and the water is somewhere near 100% saturation.

I would suspect I usually have about 3 - 4 dKH, 100 microS conductivity and pretty low BOD. By mucking about with dKH, the relative changes in pH (much larger as the water approaches 0dKH) should give you a measure of CO2 level. Unfortunately it is difficult to measure dissolved gas levels in water directly.

cheers Darrel


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## BigTom

If someone reminds me in the new year I might do a day of pH measuring on the big tank. It'd be interesting to see what it looks like. I can't measure dKH but it should still show if photosynthesis is outstripping co2 supply from surface diffusion, right?

Could run it with and without flow as well, that might be interesting.


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## dw1305

Hi all,





BigTom said:


> I can't measure dKH but it should still show if photosynthesis is outstripping co2 supply from surface diffusion, right?


 You will definitely get a rise in pH as the CO2/O2 ratio changes, just how steep that rise is, and at what level pH peaks will depend upon the reserve of carbonate buffering, as well as the depletion of CO2. There is a bit of explanation here: <http://csu-cvmbs.colostate.edu/Documents/zoological-medicine-pond-dynamics.pdf> or <https://srac.tamu.edu/index.cfm/event/getFactSheet/whichfactsheet/112/>, although in the Texas A&M sheet they use the term "alkalinity", when carbonate hardness would be more appropriate. 





BigTom said:


> Could run it with and without flow as well, that might be interesting


 That would be interesting, the difference in pH rise should give an indication of how effective the filter is in increasing the area of the gas exchange surface.

cheers Darrel


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## darren636

BigTom said:


> If someone reminds me in the new year I might do a day of pH measuring on the big tank. It'd be interesting to see what it looks like. I can't measure dKH but it should still show if photosynthesis is outstripping co2 supply from surface diffusion, right?
> 
> Could run it with and without flow as well, that might be interesting.


 party time, baby.


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