The light limiting growth management method

Tom Barr

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One typical complaint about aquatic planted aquariums by both the seasoned experienced aquarist as well as the newbie is the rate of fast growth of aquatic plants and algae. How might we control this rate of growth logically based on how plants grow? Most want good healthy growth, but just not this fast!!! So what tools do we have available to manage the rate of growth, that also helps us manage the rate of growth of algae as well? Light intensity of course.

This concept has been around for some time (but has not been really looked at critically) and states: non limiting CO2 and nutrient allow for the maximum light use efficiency at lower light intensity. Since if the CO2 and nutrients are non limiting, thus independent of influencing any reduction of growth, light will be the only factor that will control growth. This simple test is able to look at light's effects on aquatic plant growth much better than dependencies typical with many aquarists' planted aquariums that might be limiting nutrients or CO2.

Light is much more stable than CO2 or any nutrients: we can control light very easily, CO2 ppms and nutrient concentrations can move around considerably. Light is very stable on the other hand. Bulbs can be added or reduced, timed, metal screen can be added to reduce intensity to suit, PAR light meters are very simple and easy to use and testing is rarely done more than once every few years for bulb decay. Open top and suspension style lights can be adjusted to adjust the light intensity to suit any growth management desire/goal the aquarist might have.

Tropica's web site has a good effective article on the use of light and CO2 management for aquarist.
They also suggest lower light and good CO2 in their conclusion.

CO2 can also be used to reduced growth as well, but this limitation is harder to measure and control without going to a pure non CO2 addition method. Many plant species are poor competitors for CO2 and do poorly in mix communities, thus we cannot keep as many species using that method.

This is large trade off if we chose CO2 to reduce rates of growth.
Likewise, some plant species do better at lower nutrients than others.

However, most plants are fairly similar to their lower ranges of light above a certain minimum level.
This appears to be about 30micromoles/m^2/sec, there are plants that can still grow at less than 1/2 this amount, but most will do well and grow slow at 30. A range of 30-50 is suitable for most systems for slow, very easy to manage growth.
This also reduces algae growth since they are only limited by light and never nutrients or CO2 in planted tanks.

It also reduces the amount of energy required to grow plants, initial cost of adding more and more lighting.
This increase in extra light cost aquarist a lot of $ over time.

If a kW/hr is 12 cents, and the light for a 100 gallon tank is say 2x what is required to achieve 50 micromols, say 2w/gal compared to 4 w/gal, and the total is 200W vs 400 W, then 200 W x 10 hour day X 365 days a year = ~88$ a year of wasted energy, algae issues, issues with CO2 that are typically not an issue etc.

Some aquarist want to garden more during sometimes of the year or when their motivation is high, some want to reduce it due to other aspects of their life, vacations etc. If we use a bank of several light bulbs on different switches, we can adjust the intensity to suit most any goal. Many aquarist know they want nice growth that's healthy for their goal, but not weedy fast growing plants they have to prune often.

Low light is ideally suited for that goal.
Since we know light drives CO2 uptake, which drives nutrient uptake, using less light provides far more wiggle room and resiliency to management of both O2 and nutrients. Everything is much easier to care for.
This makes any goal of sustainability and stability much better. This is based on the holistic model of how a plant grows.

I would suggest aquarist try to manage a tank and slowly reduce their light intensity down.
A meter may be borrowed in many cases to target the lower ranges we know are effective. While we may be able to go even lower, 40 micromoles seems like a good range with enough cushion on the lower end and still without proving difficult or producing weedy growth.

Regards,
Tom Barr
 

Gerryd

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Tom,

Nice article. I have found lowering my light has been easier to manage overall. Thanks!

A meter may be borrowed in many cases to target the lower ranges we know are effective

My offer to loan my Apogee PAR meter is still open.....There is a thread around somewhere.

PM me if interested...
 

Biollante

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Hi All,

Great article! :)

A year ago, heck six months ago, I never would have believed lowering the light was so incredibly effective.

I have Lanceolota, Aponogeton Natans, Anubias Afzelii and some Nana all happily growing in sub 30 umol, some around 20. Lots of Sagittaria subulata at 30-35 umol. Low maintenance, low everything. :cool:

Biollante
 

jonny_ftm

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For people not having a PAR meter, like me, my tank is doing extremely well with 11W PC light at 6in above surface, on a 12 gal tank. That's 0.9wpg light. My glosso is at the bottom opposite lateral side from light, partely hidden by moss and floating cerato. Where my glosso is growing is really dark. It is carpetting so well and so slowly. Pogostemon helferi is great looking and also my anubia nana petite. My R. Wallichii is red, but under the light directly.

I dose half EI but CO2 is a mist via the atomizer and very stable.

I don't have a PAR meter, but I think I'm very low on the micromoles. So, CO2 is really the key, and low light gives a really pleasant low maintenance low problems tank, yet having all plants you like growing very healthy
 
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nipat

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Most people here in Thailand refrain from using low light.
They are afraid their stem plants will go leggy.

Is 30 umol OK for stem plants?
I don't have experience in stem plants except
heteranthera zosterifolia which doing somewhat OK
(no leggy) in low light.
 

Philosophos

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I grow stems in low light no problem; so do all the big names.

The trick is spread; multiple spaced out low watt lights. Current is invaluable as well, in fact there's a good study floating around (don't have it handy) showing that current reduces internodal space.

The real problem is a sudden reduction in light, which usually goes right along with a reduction in the number of bulbs, and therefor spread. Sudden low light coming only from above will cause shedding issues lower down on the stem and bigger gaps between nodes IME.
 

Biollante

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Bingo! As "They" Do Say

Philosophos;47067 said:
I grow stems in low light no problem; so do all the big names.

The trick is spread; multiple spaced out low watt lights. Current is invaluable as well, in fact there's a good study floating around (don't have it handy) showing that current reduces internodal space.

The real problem is a sudden reduction in light, which usually goes right along with a reduction in the number of bulbs, and therefor spread. Sudden low light coming only from above will cause shedding issues lower down on the stem and bigger gaps between nodes IME.

Hi Dan, All,

Yes as with all changes lighting needs to be reduced in steps. This is where shade cloth, screens or that neat trick Nipat had with tissue paper is important. :)

Another technique to lower lighting is the addition of floating plants or my favorite Lotus that grow and take over the surface, this seems to allow the plants to adapt as the light lowers.

The big surprise (and I am from Surprise :p) for me was not only aren't the stem plants leggy, if anything as Dan pointed out, they are more compact. :D

Biollante
 

Tom Barr

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nipat;47062 said:
Most people here in Thailand refrain from using low light.
They are afraid their stem plants will go leggy.

Is 30 umol OK for stem plants?
I don't have experience in stem plants except
heteranthera zosterifolia which doing somewhat OK
(no leggy) in low light.

Yes, many are under this assumption, not just in your country, but most other countries as well.
I think this will take a long time to remove such preceptions such as excess nutrients or PO4 will lead to algae.

These same folks where also the same ones that suggested that adding excess increased the risk of algae when the hypothesis failed on it's own. But they do not see the correlation between high excess light and algae?

Rubbish.

If you already have higher excess light, then reducing it is easy and offers no risk because you can simply revert back to high light.
If they are unwilling to test, then they need to not offer people advice based soley on their inepxierence and ignorance, no matter how nice their aquarium might look, if they have not tried it and done so a few times, then something is wrong there.
So this risk issue is not realistic at all. At worst their plants get leggy, pale etc. They bump th elight up just a little bit, then again till they have non leggy growth and good color. Thois seems to be about 30-40micromols for most plant "high demanding" species.
If the growth is compact etc and nice color, and I have low light, then somethign else must be at the root of their leggy growth other than just light. There must be some other cause they have not accounted for.

I've measured and used a PAR meter to answer how low we can go within reason. So it's a fairly concrete range, number, parameter.

It takes 1-2 weeks for most plants to gear up and switch to lower light. If you start off with low light, then there is rarely any issue. Plants need a lot of Carbon and Nitrogen to gear up for lower light. If these are added in non limiting amounts, the plant shoudl adapt very well.

Many aquarist think less is better with respect to nutrients, often waste time testing and fiddling with nutrient ppm's, hardly pay attention to CO2 as much as they likely should and then want to add too much light and do not bother to test light. This is backwards.
Then complain about stunted tips and algae.

Regards,
Tom Barr
 

Tom Barr

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Laying metal window screen works well and will not burn unlike cloth and tissue paper.
You simply add another layer to reduce the intensity step wise.

Cheap, widely available, cut to size.

Regards,
Tom Barr
 

shoggoth43

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I think you've hit this on the head. It's also rather tough to read FAMA or other magazines where they print one of your articles talking about lowering light and how higher nutrient levels and PO4 specifically do NOT cause algae while in the same magazine under the beginner questions section they talk about the need to reduce PO4 so that you don't get algae. One begins to wonder if anybody bothers to READ the magazine to see if what they're saying makes sense. Or do they think lowering light levels and upping nutrient levels to non limiting values is an "advanced aquarist" technique and dropping PO4 levels is a "beginner" method?

-
S


Tom Barr;47070 said:
Yes, many are under this assumption, not just in your country, but most other countries as well.
I think this will take a long time to remove such preceptions such as excess nutrients or PO4 will lead to algae.

These same folks where also the same ones that suggested that adding excess increased the risk of algae when the hypothesis failed on it's own. But they do not see the correlation between high excess light and algae?

Rubbish.

*SNIP*


Regards,
Tom Barr
 

Tom Barr

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shoggoth43;47082 said:
I think you've hit this on the head. It's also rather tough to read FAMA or other magazines where they print one of your articles talking about lowering light and how higher nutrient levels and PO4 specifically do NOT cause algae while in the same magazine under the beginner questions section they talk about the need to reduce PO4 so that you don't get algae. One begins to wonder if anybody bothers to READ the magazine to see if what they're saying makes sense. Or do they think lowering light levels and upping nutrient levels to non limiting values is an "advanced aquarist" technique and dropping PO4 levels is a "beginner" method?

-
S

Well, if anyone wishes to debate it, I'm game.
They will not be able to present a convincing argument, not due to me, but rather, the results of some basic test that show otherwise, same for the light issue.

Hard to beat when it works and plants grow well still.

Still, getting folks off the HLD( High Light Disease) and back to better overall management is a real key here.
Many focus more on just nutrients, a little bit, but only in the most general terms with cO2/light, not bothering to measure it critically, ironically insisting of testing the nutrients which are the easiest thing for most aquarist to keep stable and measuring indirectly.

I do not get it.

How can one hand tell the aquarium that excess/waste nutrients etc causes algae, you must test etc............then the other hand does not testing light, says to add excess wasteful amounts?

I'm not sure what or why folks give that old stale advice and what they think as far as advanced or not.......it really does not matter if they are advanced or not, it's their goal and what's the best mamanagement practice to get there that is important. Beginner vs advanced...........I do not know really......sounds like fear based advice, not based on any test of any sort, just some correlation and myth from the past.

There's no such risk.

Regards,
Tom Barr
 

jonny_ftm

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Here's my 12gal, 0.9wpg tank, full of CO2 mist, 185gph filter, 3ppm PO4/week, 15ppm NO3/week, 6.5ml TPN/week and soon some DTPA. I'm lean on NO3 but it works well to manage less waterchanges.

P. Helferi was recently completely rearranged in more spaced plantlets. They should soon evolve as a large flower better looking then when densely planted. Glosso on the right is carpetting slowly but securely and without any melting despite its very dark situation, far from light. Glosso is also getting tons of CO2 mist and it perls nicely. Rotala Wallichii is dense, red and with many side shoots. I never retop it, only trim and throw away the tops.






Here's how it looked before trimming the P. Helferi, really dense. That's 0.9wpg, no PAR meter though, but should be very low PAR




When P. Helferi grows again and the glosso finishes carpetting, it should look much better
 

Biollante

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Wow! Once Again

Hi Jonny,

That is very nice. :cool:

On the right toward the back I am sure that is less than 20 umol and I can see growth. :)

Biollante
 

jonny_ftm

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On the back right side, where in the first pic you see a "dark hole" there are some anubia nana petite growing. You can see them if you focus on the darkes part of that spot. It's incredible where they are growing, just at the roots of the Java fern, with a dense layer of floating cerato on surface above them. What is surprising me the most, is the glosso carpetting in that front right side.

I forgot to say: all this thanks to the barrreport and Tom advices, I'm so gratefull for these results as my 2nd tank. Later, I could focus on my scapes, now that I managed algae when starting tanks
 

Wet

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Rad tank and a strong argument for this method, Jonny.
 

Tom Barr

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jonny_ftm;47159 said:
Well, suerely DSM helps a lot here, at least enriched organic soil

But that only supports the method more:)
It rules out CO2 and nutrient limitations.

So then you are left with light as the dependent variable, rather than having confounding issues with CO2/nutrient that affect light.
This is fairly dramatic, a 600% different or more in growth according to Tropica's test using Riccia for a non CO2 system,, and only 300% difference with CO2.

So you have around 200% the reduction in growth when CO2 is dependent. This likely varies from 5% up to 200%, not including algae issues etc. Think that plays a role in various aquarist results?

Still, at lower light, this % will be reduced and come closer to zero % if CO2 is used correctly.

Regards,
Tom Barr
 

jonny_ftm

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Yes, even in this very low light low maintenance setup, I keep CO2 on the very high side. Maybe it explains the excellent growth I have despite the extreme low light
 

Tom Barr

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jonny_ftm;47178 said:
Yes, even in this very low light low maintenance setup, I keep CO2 on the very high side. Maybe it explains the excellent growth I have despite the extreme low light

Yes, less plant resources are going to acquire CO2(non limiting, rich amount), so virtually any excess resources can be allocated to light gathering that may had gone to acquiring limited CO2. If the tank had strong CO2 limitation AND strong light limitation together, then the light would have to be higher, perhaps 2-3x as much.

Regards,
Tom Barr