# Consequence of short photoperiods



## gf225 (Mar 26, 2005)

Is there a general accepted minimum photoperiod for plants? 

I seem to remember reading most plants not "registering" less than 4 hours, even though my plants pearl within the hour (riccia in minutes). I assume that pearling doesn't necessarily mean there's enough growth for long-term plant health i.e. 1 or 2 hour photoperiods wouldn't work - or would they!?

I ask because I wonder if there's more benefit to lower photoperiods, especially with higher lighting. I assume there would be more room for error with regards dosing and algae. Less CO2 consumption would save $£ too (on a solenoid).

Let's assume we want less growth for maintenance purposes, but still wish to grow demanding plants so need higher light intensity. We could run lots of light for a shorter period yet still minimise algae. The midday halide burst springs to mind. 

Assuming we keep on top of CO2 and other nutrients then surely lighting duration has to be a factor towards algae control, as long as there's sufficient photoperiod for plant growth of course.

I have a 2.5 gal. nano with 24w PC T5, not really high light but enough to grow hairgrass and riccia like there's no tomorrow. I'm currently running 8 hours but wonder if I could get away with a lot less. I don't like to limit nutrients to control growth, and I can't adjust light intensity. Short photoperiods seem the ideal answer.

Your thoughts most welcome.


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## hoppycalif (Apr 7, 2005)

I don't know the answer to your question, but I have noticed that most people want the lights on period to be long enough for them to enjoy the tank when they want to. Once you drop down to 4 hours or so, that becomes a problem.

If there are botanists among us, perhaps there are studies or theories that say what the minimum effective lighting period is?


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## gf225 (Mar 26, 2005)

Thanks for the reply Hoppy. The tank's in the kitchen so I don't see it much, it's more an experimental aquascaping tank.


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## redstrat (Apr 3, 2006)

couldn't hurt to give it a shot for a couple weeks, I bet the plants would spring back pretty quickly if they were given a longer photo period if it got to be to short for them.


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## excaliborg (Sep 18, 2006)

My tank usually had around 10 hours of light a day. However, I've had to leave the tank for 2 weeks without being able to access it as I'm away. Gave the tank a water change and reduced the photo period to 5 hours. Not looking forward to how it's going to look when I return  . I Hope limiting the photo period will have limited the amount of algae though.


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## Jason Baliban (Feb 21, 2005)

I have run my higher light tanks as low as 6 hours for a couple months. Things grew very slow. I still take this approach when i have a new tank, at least for the first few weeks.

jB


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## gf225 (Mar 26, 2005)

Thanks for the replies guys. Once the scape has reached its "peak" I'll give 4 hour periods a shot, and report back my results of course.

excaliborg - what spec is the tank? Your results will be interesting.


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## Edward (May 25, 2004)

We don't know what the minimum is. But I am very interested in such experiments. Currently, I am running 250 Watts MHs on 24" high aquarium for just 5 hours. Plant growth and quality is great. Heavy pearling with CO2 addition.


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## BryceM (Nov 6, 2005)

On my 180g tank I use 0.9 wpg of T-5 lighting with TEK reflectors for 10 hours per day. In the middle of this I use an additional 2.5 wpg of MH lighting for only 4 hours. Growth in the tank of A. renekii, R. vietnam, L. 'cuba', and HC is explosive. I'd actually like to slow it down.


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## niko (Jan 28, 2004)

I have a CO2-supplied 35 gals. tank that I kept with 2 hours of 96 watt CF for about 4 months. I did that out of laziness as a lazy way to fight algae. The tank is in a room with no windows so when the tank light is off the plants are in complete darkness.

** Tank has only cherry shrimp, no fish. 

**CO2 is disolved with a powerhead (Dueto filter, 1 to 1.5 bps)

** Substrate is 1/2" - 1" of garnet (basically quartz). 

** GH/KH are 2-3. 

** No fertilization during the short light periods. 

** WC - 10% every 4 days (once a week for maybe 2 or 3 weeks total). 

** WC are done with water run tru activated carbon.

**Plants:

- Blyxa japonica
- Echinodorus tenellus
- Marsilea sp.
- 4 kinds of mosses
- Narrow leaf Java Fern
- Cuba
- Hygrophilla angustifolia
- Hygrophila corymbosa
- Anubias nana "eyes"
- Echinodorus latifolius
- Valisneria nana
- Riccia
- HC (in a corner where the light is very low)
- Stargrass
- Ludwigia sp.
- Lagarosiphon madagascariensis
- Crypt green gecko
- Crypt green gecko, darker variety

When the light period was reduced to 2 hours the plants stopped growing and quickly started to look ugly. But most of them did not die. The Lagarosiphon died in about a month. HC died about month 3. Riccia grew small, dense and pale. H. corymbosa barely grew 1 small leaf about every 2 weeks. Algae disappeared completely. 

Basically I got a clean tank full of ugly plants. I upped the light period to 4 hours for about 2-3 weeks. Nothing changed probably because I didn't fertilize at all. I upped the light to about 6 hours a day for 3-4 weeks - the mosses started to grow very slowly, all other plants very much stayed the same. 

The tank never got algae again even when the light period was upped to 10 hours. At that time I started to fertilize very lightly once a week. The plants took off - every 2 weeks I must trim. I don't even have to wipe algae off the glass - the tank is completely void of them except a few tiny BBA areas on the JF roots and the filter outtake that never spred and never grow taller than 1/16".

What did I learn? Nothing much, other than that with CO2 and small frequent water changes even extremely short light periods do not kill many plants.

I do know though that if the CO2 is shut off the plants will not survive well with a short light period.

--Nikolay


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