# co2, ferts/nutrient, light imbalance question



## crice8 (Aug 2, 2012)

jcmv4792 said:


> If there is high light, but low co2 and low amount of nutrients in the water. Why is there still algae growth? Does algae use O2 instead of co2?
> 
> And do all combinations of imbalance(low light, high co2, low ferts...etc) cause algae problems?
> 
> ...


High light requires high co2


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## Raymond S. (Dec 29, 2012)

Balance.
Light gives energy which is needed by plants to grow. Algae is a plant.
Since it is a one cell plant, it requires far less nutrients than regular plants do.
Add lots of light and something is going to grow.
Whichever has the most of it's necessary nutrients will grow best.
http://www.plantedtank.net/forums/showthread.php?t=107303#2


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## plantbrain (Dec 15, 2003)

Management wise: the more light= the more CO2/nutrient demand from the plants.

Less light/lower light= easier to manage CO2 and ferts. 

Those factors and plant growth are the issue, and when those are not addressed(plant growth factors) then.............you get algae. 

High (or low) Ferts are NOT the factor, we have cases(plenty) where there's high ferts, high light and CO2........no algae..............

We also have cases where there's low light, high ferts and no algae.
Thus one can conclude: ferts cannot be the cause of algae independent of other factors. 

Most folks run out and buy high light, that's the 1st mistake. 
Then they have troubles from there and rarely get rid of the light and get a lower much more manageable light/intensity. Plants still grow at low light, they just grow slower.


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## Doppelgaenger (Jul 20, 2015)

too high a light with not enough nutrients provided will starve plants and the extra light will be used by the one thing that doesn't need that much in the way of nutrients to grow, which is algae.

The equivalent is a tank full of starving fish that will die, but in the meantime the shrimp on the bottom are still eaking out a living eating the biofilm


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## mattinmd (Aug 16, 2014)

Tom will probably correct me on this, but this is my own personal hypothesis on the matter.

Facts: 
To make sugar, plants need light, co2 and water. CO2 supplies are very limited in low tech tanks. Certainly water is plentiful, and we can readily control lighting.

As light levels increase, most plants are going to produce more sugar, thereby consuming more CO2 and water. 

True Algae (not cyanobacteria or Diatoms) is a plant, and it also uses the same basic materials as any other plant. However, algae is a very simple, primitive plant.

Technicalities: Technically, there's a limit beyond which the plant stops using more light regardless of CO2 and water availability, but I'm going to assume we're not hitting that limit for the plants at hand.

Thus: Assuming there's no CO2 injection going on, as you increase light, the plants are at some point going consume CO2 faster than it can diffuse into the tank from the air and eventually to drive CO2 concentrations down to a point that they can no longer extract CO2 from the water. Increasing light beyond this point is of no value to the plants, as they are now carbon limited. 


*Unproven wild hypothesis part*: I suspect that algae, due it its primitive nature, is able to absorb CO2 at lower concentrations than plants are, and will flourish in environments where the light is bright and plants are carbon limited.

However, that's an unproven idea on my part. There's a lot we don't really understand about the growth of algae.. Why does vigorous plant growth suppress algae? Why does algae seem to flourish whenever the plants become limited by some form of deficiency (carbon or fertilizer based)? These are both deep questions that AFAIK modern science doesn't yet have the answers for.

edit:

I should also note this is a pretty simplistic approach, and the true answers are probably much more complicated. However, usually in nature when you see one organism flourishing while others are not, that organism is somehow better adapted to the conditions.


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## mattinmd (Aug 16, 2014)

So, doing some digging, I found at least one paper that suggests that micoalgae and cyanobacteria are able to concentrate CO2, and thus efficiently extract CO2 from a CO2 defficient environment.. 

It seems to suggest that some higher plants appear to have a similar ability, but not all..

http://www.plantphysiol.org/content/119/1/9.full.pdf

Regardless, if algae have a lower minimum useful CO2 concentration, that would explain a lot...

Once the concentration drops below what plants can use, algae would then drive it lower... at that point, they are going to keep the concentration down at their minimum, effectively cutting the plants off from all CO2 for the remainder of the daylight cycle..


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## Xiaozhuang (Feb 15, 2012)

I agree with the general statement that lower lighting levels gives much easier management as a whole. Probably the best advice for newer aquarists.

That being said, I leave these examples where its high if not very high lighting levels (70 PAR to >100) on low tech tanks that are clean of algae... If algae functioned on such linear mechanics why are these tanks so clean?


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## jcmv4792 (Jul 15, 2015)

Impressive as always! 

Wouldn't your method/philosophy only apply to low-tech tanks with soil as the substrate though?(since you said you have low expectations for tanks with inert substrate). 

I know 70 PAR might be a bit much for me(since I'm both new to this, and using eco instead of soil), but what I'm curious about is if I could get away with PAR levels slightly lower than that in my particular setup(I'm thinking 50-60 PAR).

I understand one of the factors are what plants I use, and how I set it up.

This is pretty much the entire list of plants I have or have ordered so far. Do you reccomend I omit any of these plants in the setup I am after? Or would you say for now, just stick to "low light" and forget the higher par:

- Stauro repens
- giant hygro
- hygro stricta(compact)
- hygro semiensis
- dwarf hairgrass
- pygmy chainsword
- marsilea hirsuta
- crypto parva
- ludwigia repens
- golden lloydiela
- Alternanthera reineckii roseafolia


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## mattinmd (Aug 16, 2014)

Xiaozhuang said:


> I agree with the general statement that lower lighting levels gives much easier management as a whole. Probably the best advice for newer aquarists.
> 
> That being said, I leave these examples where its high if not very high lighting levels (70 PAR to >100) on low tech tanks that are clean of algae... If algae functioned on such linear mechanics why are these tanks so clean?


Yeah, I agree it is an over simplistic approach, and was to some degree thinking of you when I said that at the end of my earlier post...

There's a lot to consider here that could change the exact PAR level that problems show up at.. Certainly CO2 is supplied by exchange with the air, but also from the bacteria in the substrate and biofilter.. Things like excel complicate maters further by suppressing algae and (slightly) increasing carbon supply.

The selection of plants is going to matter too.. The idea I'm proposing only triggers if the CO2 in your tank drops below a concentration that is usable by *ALL* desirable plants in your tank, but is still above a concentration usable by algae. If you've got something in your tank that can utilize CO2 at the same levels as algae, it can still compete with them for CO2, and this effect can't happen.

So we can make generalizations about "don't go over 35 PAR in low tech" but we all know the actual levels are much more complicated... That level itself is based on a well planted tank with at least some fast-growing plants (possibly fast growers are better CO2 absorbers?). Certainly we all agree a low-tech tank with 2 anubias plants in it will more readily grow algae than a low-tech tank full of fast growing hygros, ludwigias, myrios, etc..

Of course, none of this applies to high-tech... and it is also a highly simplistic view of what is likely a complicated system...


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## Xiaozhuang (Feb 15, 2012)

I agree with your approach actually, mattinmd - I think most of your posts in general are based on pretty good research/hypothesis. 

I think my tanks are clean in spite of the high-lighting - not because of it. (though I claim the higher lighting levels allow one to grow carpets better/more healthily). I think that in such cases, the overriding factor is competitive plant mass covering most of the available surface, combined with low bio-load, such that algae does not have a favourable spot to bloom/latch onto. I may get hair algae in the uncovered HOB for example, but it doesn't grow in the tank. In tanks where I have low lying stones, they remain clean. However, when I have a pinnacle that rises above the plant mass reaching a height say an inch from the water surface, then I get green dust/spot algae only at that spot. These are anecdotal observations though 

I think these are sure/very high rate of success even with lower PAR

- giant hygro
- hygro stricta(compact)
- hygro semiensis
- marsilea hirsuta
- crypto parva
- ludwigia repens
- golden lloydiela

These are questionable / Do much better with CO2/better conditions / may succeed with consistent effort/luck

- Alternanthera reineckii roseafolia (to grow it well, not just survive)
- dwarf hairgrass (grow in decent time)
- pygmy chainsword
- Stauro repens


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## mattinmd (Aug 16, 2014)

Xiaozhuang said:


> I agree with your approach actually, mattinmd - I think most of your posts in general are based on pretty good research/hypothesis.


Thanks...

In the long run, there is an experiment that can be run to prove some of this out. Testing to see if modest CO2 levels, if maintained well, can prevent algae outbreaks under high light.

If you have a setup that can maintain a rock-solid 10ppm CO2, ie via pH controller, with good enough flow in the tank to avoid "dead spots", stocked with low-tech suitable plants is this sufficient to allow you to crank the lights up really high without algae?


If that theory holds, 10ppm should be enough to keep low-tech suitable plants growing.. maybe not at the highest rate possible, but you won't get into any situations where algae can undercut the CO2 supply, and shouldn't run into algae issues.

This goes against the conventional approach of trying to hit 30ppm, as that's what's needed for some high tech plants.. but the idea here isn't about getting high-tech plants to grow their best.. it is about seeing if a modest CO2 level can keep algae at bay...




Xiaozhuang said:


> I think my tanks are clean in spite of the high-lighting - not because of it. (though I claim the higher lighting levels allow one to grow carpets better/more healthily).


I think your tanks are clean due to experience that leads you to already know what is likely to work...

I for the life of me can't get 40 PAR to go without algae problems, hence my series of dimmer-hack-in projects..


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