# Par and Time



## BruceF (Aug 5, 2011)

One of the things that seems to get lost in all this light discussion is time. I am using a very bright 12 inch finnix fixture right now on a 10 g tank. I've pushed the amount of on time back now to 9 hours and I probably will need to reduce it more. There are not a lot of plants in there as I tend to grow my tanks from cuttings. I am not using any co2 but I do feed all my tanks fairly regularly. 

I know the time requirements of the most demanding perennial plants is about 6 hours of direct sunlight. I doubt most aquatic plants get more than that on any given day and it seems like restricting the light to just 6 hours and having the light be intense might just work fine. I assume the added benefit might just be the this period is too short for moist algae but I don't know if that is true. 

I am curious if anyone is doing something similar.


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## Maryland Guppy (Mar 5, 2015)

FWIW I run a 6.5 hours full intensity photoperiod.
Ramp up time is 15 minutes, ramp down time is 30 minutes.
A total of 7 hours & 15 minutes.
Moonlight doesn't count for plants since they close up physically for the night.
Can the very low PAR moonlight grow algae, I don't know.


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## Michael (Jul 20, 2010)

Traditional wisdom is that one can compensate for low PAR by increasing photoperiod, within limits of course. And inversely, algae problems from high PAR can be solved by decreasing the photoperiod.

I don't know of any science-based evidence for this. But as I switched from poor fluorescent lights to better LED lights on my Walstad tanks, I definitely needed adjustments to photoperiod to avoid algae growth, among other methods.


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## hoppycalif (Apr 7, 2005)

This is what I know about this subject:

Both the photoperiod and the intensity of the light affect plant growth. All plants require some minimum light intensity to grow at all, and that varies from species to species. Once you have enough intensity for growth to occur, the amount of growth you get per day depends on how long the photoperiod is. But, there is a maximum photoperiod for most plants too - a longer photoperiod causes no increase in growth beyond some limit, and that limit isn't the same for all plants.

Since light intensity determines the rate of growth of all plants, the nutrients available to the plants must be adequate to support that rate of growth, or added intensity does not increase the rate of growth.

I consider intensity and photoperiod to be independent variables, so you can't substitute photoperiod increases for intensity increases.


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## TropTrea (Jan 10, 2014)

Going back at least 10 years there was a university study in exactly this. If I recalled they used multiple T-5 bulbs on large tanks then measured the plant growth with different number of bulbs burning for different time spans.

What they did find was each lighting combination of bulbs had its sweet spot as far as time goes. If you varied either way from that sweet spot you decreased plant growth. However excessive lighting can not be compensated efficiently by shorter times by and get the same growth rate. Or can lower lighting levels be compensated by longer time periods efficiently. 

The other think I remember mentioned was they used three different plants from different natural latitudes. From that they determined that the ideal timing varied more so than intensity.


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## BruceF (Aug 5, 2011)

Growth rate isn't a problem unless it results in an algae problem. So really it is the algae problem that I am addressing. The hot thing in weed growth right now is 24/7 high intensity led light at the perfect setting. The growth rate is phenomenal. Under water however that will just lead to one huge mess.


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## hoppycalif (Apr 7, 2005)

People use high PAR lighting and don't get algae problems. People use high PAR lighting and can't stop BBA from taking over their tank. People use medium PAR lighting and still can't stop BBA from growing. People use medium PAR lighting and don't get algae problems. Clearly there is a lot more to avoiding algae than just using lower light intensity.

There are so many variables that determine what your algae situation will be that I doubt if it is possible to change only one of those variables and reliably not have algae problems. I think we just have to be as aware as we can of what the variables are and how to keep all of them out of the algae prone territory all the time.

Some of the variables are:
light intensity
photoperiod length
CO2 concentration 
water movement
plant health
organic debris
etc.


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## BruceF (Aug 5, 2011)

Hoppy I think it is safe to say that everybody has algae problems.


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## hoppycalif (Apr 7, 2005)

BruceF said:


> Hoppy I think it is safe to say that everybody has algae problems.


Algae is probably a nuisance everyone has, but I know many people handle it routinely, so it isn't a problem. BBA can drive people to quit the hobby! That's what I consider a problem.


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## Michael (Jul 20, 2010)

I never have any algae. I also walk on water.


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## BruceF (Aug 5, 2011)

Useful skill Michael.

I saw a tank a few weeks ago with BBA. I told the owner to nuke it with H2O2. I saw it again the other day and the algae was gone.


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## hoppycalif (Apr 7, 2005)

Michael said:


> I never have any algae. I also walk on water.


When I tried that my shoes got wet.


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## TropTrea (Jan 10, 2014)

BruceF said:


> Growth rate isn't a problem unless it results in an algae problem. So really it is the algae problem that I am addressing. The hot thing in weed growth right now is 24/7 high intensity led light at the perfect setting. The growth rate is phenomenal. Under water however that will just lead to one huge mess.


24/7 lighting regardless of how bright or dim goes 100% against everything I learned in Botany and my past experiments in finding the perfect lighting balance. Every plant has both a photosynthesis and a respiration period. Light is required for photosynthesis.

Studies that I had done on light cycle showed different results with different intensities. by measuring the Oxygen created from the plant. The numbers looked like this for trend data only.
time lights on lower light high light
6 hours 8 12
7 hours 9 14
8 hours 10 16
9 hours 11 17
10 hours 12 18
11 hours 13 18
12 hours 14 19
13 hours 15 19
14 hours 15 18
15 hour 16 18
16 hours 15 17
17 hours 14 16
18 hours 12 14
19 hours 10 11

note with the lower lighting the ideal was 15 hours of light while with the higher lighting it was 12 hours of lighting. Note the different plants species we used gave us different ideal times, as well as differences in the optimum amount of light for max growth. We also found various studies on this from other groups showing similar data when only these two variables were changed.


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## TropTrea (Jan 10, 2014)

Michael said:


> I never have any algae. I also walk on water.


Actually my Algae issue went to near zero when I started building my own LED lights. But I attributed it partly to the design of the light LED work as miniture spot lights. When the front row is angled back at about a 30 degree angle there is very little light from them which hits the actual front glass.

The other thing that help keep algae under control are called Bristle Nose Pleco's. For the last 15 years I try to keep at least a pair in every one of my tanks. Sometimes they breed for me and I have more for future tanks.


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## BruceF (Aug 5, 2011)

Thanks TT. I am sure you know better than I do. I tend to avoid fish that multiply rapidly but I've been adding ancistrus recently.

https://www.420magazine.com/forums/vegetative-cycle/63944-photoperiod.html


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## TropTrea (Jan 10, 2014)

BruceF said:


> Thanks TT. I am sure you know better than I do. I tend to avoid fish that multiply rapidly but I've been adding ancistrus recently.
> 
> https://www.420magazine.com/forums/vegetative-cycle/63944-photoperiod.html


Please not that article is talking abut one specific terrestrial plant that has extreme lighting requirements. The experiment we did and other experiments we reviewed showed us that different plants preferred different lighting levels s well as different photo periods.

It is almost like comparing a Nesaea species of plant with a Crypt plant your trying to get to flourish in the same small tank.


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