# Why does ammonium and ammonia cause algae?



## mattinmd (Aug 16, 2014)

A quick Google search suggests that algae spores can absorb ammonia as a nutrient, but not nitrate. The same sources suggest mature algae can derive from either. This is comparatively new information to me, but I find it interesting.

If this is true, ammonia/ammomium is critical to the development of algae from spore into a mature organism. Without ammonia, new algae spores would be nitrogen deprived and would fail to develop, or develop poorly/slowly.

Of course, your plants and bio-filter are going to compete with the algae for ammonia. If they are taking up the ammonia fast enough, there should be very close to 0 ammonia in your tank. However, even with 0 ammonia in the tank, that doesn't really mean your plants and filter are getting all of it. It is a competition after all, and if you have mobile life forms in your tank, they will make ammonia and the algae will absorb some of it. 

All we can do is try to tip the scales so that there's more competition from the filter and plants, reducing the percentage the algae gets. 

It is interesting to me in that it would suggest why vigorous plant growth stiffles algae, even when we supplement NPK+Ca+Mg+S+Fe+micro+co2 in mildly excessive levels (EI dosing). We have to be starving the algae of something it needs, and if we add an abundance of all these nutrients it has to be something else. Yes light is a factor too, but rapid plant growth can't really steal light from algae in areas not shaded by their leaves.


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## plantbrain (Dec 15, 2003)

NH3/NH4 does not appear to cause algae at moderate to lower levels, say 1.0 ppm to 0.8 ppm is a well run planted tank. 

No planted tank will demand more than that daily dosed amount however.

Algae spores germinate based on evolutionary cues, this may or may NOT have anything to do with ferts/access. Algae tend to be well adapted for seasonal changes and changes in general. Submersed Aquatic plants tend to be better in more stable systems. Plants need a lot more nutrients than algae to grow. 10-1000X more. 

We feed fish and that produces NH4, plants take that directly. 
But there's ample access by algae to this same pool of NH4. 

I was able to induce GW in several tanks about 15 years ago with NH4CL. But the GW might have been due to CO2 issues or a very limited filtration. NH4 might have tipped the scales and caused a bloom(dependency on poor CO2, suboptimal levels etc). I cannot rule that out. I and others have added NH4 without too much algae issues, so the hypothesis is falsified.


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## mattinmd (Aug 16, 2014)

Fair enough. The idea was interesting while it lasted... 

I guess if it were true we'd all have massive algae blooms during fishless cycling at 4ppm NH4.... I had diatoms and some very minor staghorn at that time, but not much else.


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## 691175002 (Apr 28, 2009)

What exactly does cause algae? It seems like any factor when tested alone does not cause algae.

If you took a healthy tank and removed all plants (and reduced fertilization to maintain healthy levels) algae would take over, yet allelopathy is not a significant inhibitor in the aquarium.

Are plants just faster at grabbing nutrients that briefly escape from their chelated states?


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## Hoppy (Dec 24, 2005)

691175002 said:


> What exactly does cause algae? It seems like any factor when tested alone does not cause algae.
> 
> If you took a healthy tank and removed all plants (and reduced fertilization to maintain healthy levels) algae would take over, yet allelopathy is not a significant inhibitor in the aquarium.
> 
> Are plants just faster at grabbing nutrients that briefly escape from their chelated states?


Algae have been around for at least millions of years. Aquariums have been around for less than 1000 years. It follows that algae evolved with no evolutionary pressure from aquarium habitats. Doesn't that mean that our planted tank algae are "caused" by nothing related to aquariums? Algal spores exist virtually everywhere, so maybe the "cause" is algae spores in our tanks?


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## 691175002 (Apr 28, 2009)

Hoppy said:


> Algae have been around for at least millions of years. Aquariums have been around for less than 1000 years. It follows that algae evolved with no evolutionary pressure from aquarium habitats. Doesn't that mean that our planted tank algae are "caused" by nothing related to aquariums? Algal spores exist virtually everywhere, so maybe the "cause" is algae spores in our tanks?


My question is closer to why does the presence of healthy plants inhibit algae?

It cannot be competition over nutrients, since we ensure they are always in excess.
It cannot be competition for light, since algae can just float in the water or grow on the glass.
It cannot be allelopathy, since neither activated carbon nor waterchanges (which both remove allelopathic compounds) do not cause algae.

I know the common response is that a single factor being out of balance will cause algae, but I am confused as to how an excess of a single nutrient is different from an excess of every nutrient.


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## Fishly (Jan 8, 2010)

Hoppy said:


> Algae have been around for at least millions of years. Aquariums have been around for less than 1000 years. It follows that algae evolved with no evolutionary pressure from aquarium habitats. Doesn't that mean that our planted tank algae are "caused" by nothing related to aquariums? Algal spores exist virtually everywhere, so maybe the "cause" is algae spores in our tanks?


The question is not "where does algae come from?", the question is "why does algae break out in some tanks but not others?"

We know that algae needs some things to survive, like nutrients, carbon, and light. So, why, when we dose all these things in excess, do we not get algae? Why, when we seem to have all these things under control, do we still get an outbreak?


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## Hoppy (Dec 24, 2005)

Maybe algae have not done well growing on healthy, fast growing plants over the millenia. So, evolutionary pressure has led to algae which doesn't start growing unless unhealthy, or few plants are growing. The principle of evolution is that traits that give a reproductive advantage tend to be favored, and those that give a reproductive disadvantage tend not to be favored (in other words more individuals will reproduce among the first group than among the second group.) So the specimens of algae that now exist are almost all those which don't even attempt growth unless there are few or unhealthy plants growing.

There are many types of algae - some do float freely, but many anchor themselves in one spot. BBA and GDA are each distinct species of algae. GDA does float, and even "swims" around, but BBA stay anchored. We tend to discuss algae as a single pest, but it is really a big family of pests, only kissing cousins, not siblings. Each has it own requirements that must be met before they start growing.


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## fablau (Feb 7, 2009)

plantbrain said:


> Algae tend to be well adapted for seasonal changes and changes in general. Submersed Aquatic plants tend to be better in more stable systems.




I think what Tom said above is key. After several years of planted aquarium keeping, I also agree on the fact that stable systems favorite plants growth whereas unstable systems favorite algae. It is compelling though how plant and algae growth are inversely proportional with each other. When plants thrive, algae struggle and vice versa.

Fertilizers? Over fertilizing? Not a problem if plants thrive... But if plants struggle, they may contribute to algae growth.

Take this example: you have a well balanced tank, with excess nutrients for plants, then plants thrive and algae are not present. Start messing around, maybe providing, let's say, not enough PO4... After a while GSA could appear... Here's the imbalance which would cause some plants not to growth to their full potential, hence algae. Same issue if you are too lean with No3 compared to the other nutrients... Plants struggle, algae take over.

Another example: I started having BBA when my Co2 wasn't constant and stable. Either my old durso overflow was splashing too much or I tried to keep the "perfect" ph drop by turning on/off the co2 with the solenoid via controller, my co2 wasn't "stable all the time"... Then, plants suffered and algae took over... Better to have a lower co2, but stable co2, without interruptions! Stability: plants thrive, algae suffer.

Here's another story: Besides 4 planted tanks, I own a small pond with lilies, water lettuce, hornwort and elodea... And I couldn't get rid of filamentous algae despite those plants were growing petty well. Yes, the tank gets a ton of direct sunlight, but most of the surface is covered by plants (90-95%)... So, what else? Well... Turns out that after testing Po4 and No3, tank had 0ppm No3 but over 3ppm Po4, consistently, all the time! No idea where that Po4 was coming from... Maybe from the soil of the lilies or other plants in pots? No idea... Well, I started adding No3 and proportionally micros, and therefore Po4 levels dropped because plants could finally absorb all nutrients (Liebig's law), and.. Guess what? After a couple of weeks algae disappeared! So... What was causing algae? Excess Po4? No, really... Was the lack of the other nutrients that was starving plants in some way, and algae thrived!

Does all this make sense??


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## Zapins (Jan 7, 2006)

691175002 said:


> My question is closer to why does the presence of healthy plants inhibit algae?
> 
> It cannot be competition over nutrients, since we ensure they are always in excess.
> It cannot be competition for light, since algae can just float in the water or grow on the glass.
> ...





691175002 said:


> What exactly does cause algae? It seems like any factor when tested alone does not cause algae.
> 
> If you took a healthy tank and removed all plants (and reduced fertilization to maintain healthy levels) algae would take over, yet allelopathy is not a significant inhibitor in the aquarium.
> 
> Are plants just faster at grabbing nutrients that briefly escape from their chelated states?


I agree with your points. I think deficiencies and toxicities, allelopathy, shading, etc are the dominant algae controlling factors in planted tanks.

Here is what I believe causes algae outlined in an organized way (a bit of a long thread to be sure). Let me know what you think.
http://www.plantedtank.net/forums/showthread.php?t=679601

To answer the OP's question why ammonia in planted tanks? Ammonia damages most of our plants which reduces their effectiveness at controlling algae. Plant damage from ammonia occurs around the 1-2 ppm range. Long term, lower ammonia levels probably also negatively affect many aquatic plant species, so I wouldn't recommend using it as a source of nitrogen.


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## plantbrain (Dec 15, 2003)

691175002 said:


> My question is closer to why does the presence of healthy plants inhibit algae?
> 
> It cannot be competition over nutrients, since we ensure they are always in excess.
> It cannot be competition for light, since algae can just float in the water or grow on the glass.
> ...



Why does algae and nutrients define the system rather than plants, where present in sufficient biomass, control and modify the system?


There is top down ecosystem control and bottom up ecosystem control and good examples of both in nature. 

Why do weeds not take over farmer's fields?
Similar reason aquatic plants grow well and we do not have algae when we grow and focus on the plants.

The real question for hobbyists is why not focus on your goal: growing the plants well? Then the algae question is/becomes much less interesting.
If there is one thing that all people who do very well in this hobby, good at scaping and nice tanks have, it's that trait. A strong focus on the plant's needs, not the algae's.


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## plantbrain (Dec 15, 2003)

Zapins said:


> I agree with your points. I think deficiencies and toxicities, allelopathy, shading, etc are the dominant algae controlling factors in planted tanks.
> 
> Here is what I believe causes algae outlined in an organized way (a bit of a long thread to be sure). Let me know what you think.
> http://www.plantedtank.net/forums/showthread.php?t=679601
> ...


So why don't ADA AS tanks kill plants when newly started up aquariums have higher ppm's of NH4? I was only able to induce Green Water.

I was able to induce a host of common algae when I progressively added more and more minnows to a 25 Gallon tank, but the O2 levels also dropped, I had about 200 (2-3 inch fish) in a 25 Gallon tank and had relatively low plant biomass, but the tank was very healthy and had algae eaters. Then I got Green water 1st, followed by Staghorn and then BBA later. 

So perhaps a combination of O2 being lower, organic loading and NH4 from the organic load versus say from an inorganic source. There's some correlation with all of these things, but is one of them the smoking gun? Not really. 
I do know I can reproduce that same test with more and more fish, and so can most people if they are willing.

Folks have added urea and NH4 for sometime in the water column. There's just little need to lard on more than 1 ppm(people tend to be more careful with it than NO3 as well). I think the ADA AS has a lot of peat and removes the alkalinity, this shifts the algae to more a diatom based community, at least for awhile. After a month or two, then this effect seems to wear off. But so does the NH4 leaching and the bacteria colony is pretty active, as is plant growth by then. 

I'd say herbivores and algae eaters do a lot of the cleaning of aquatic plants in FW and marine seagrass beds. In Florida, most all the nicer rich CO2 springs had loads of snails, Billions of them. There's an old diagram of sunfish that eat snails/zooplankton and bass that eat sunfish, in planted systems where after adding the bass, the water starts to get nice and clean and the populations of the snails and zooplankton shoot way up, and the sun fish populations drops. Classic top down control. Do not discount algae eaters.

Carpenter's paper/s are the basic reading for these types of ecological concepts. Cited 866 times, might be a good paper to read. 

http://www3.nd.edu/~underc/east/publications/documents/CarpenterandLodge1986.pdf


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## plantbrain (Dec 15, 2003)

fablau said:


> Here's another story: Besides 4 planted tanks, I own a small pond with lilies, water lettuce, hornwort and elodea... And I couldn't get rid of filamentous algae despite those plants were growing petty well. Yes, the tank gets a ton of direct sunlight, but most of the surface is covered by plants (90-95%)... So, what else? Well... Turns out that after testing Po4 and No3, tank had 0ppm No3 but over 3ppm Po4, consistently, all the time! No idea where that Po4 was coming from... Maybe from the soil of the lilies or other plants in pots? No idea... Well, I started adding No3 and proportionally micros, and therefore Po4 levels dropped because plants could finally absorb all nutrients (Liebig's law), and.. Guess what? After a couple of weeks algae disappeared! So... What was causing algae? Excess Po4? No, really... Was the lack of the other nutrients that was starving plants in some way, and algae thrived!
> 
> Does all this make sense??


This hits on what I call *reverse* alleopathy, not so much what a healthy plant releases that's the cue for algae, rather, *what a stressed plant and decaying plant releases.*

Those stressed released chemicals/impacts do not inhibit algae, they encourage it. 



Carpenter's paper hits upon this a little bit. See page 347, DOC release is most rapid in the early stages of decay. Decay is mostly NH4 as far as N is concerned. Lowering of O2 is also a common issue with poor plant growth.

Aquarist also do not realize or know that their plants are not optimal or limited many times. So increased DOC+NH4+ lower O2 all correlate with poor plant growth. Many aquatic plants tend to respond by auto fragmentation/leaf loss to poor conditions or changes. This reduces any sinks of for resources and sends the fragments out in hopes of finding a better location to grow. Algae do a similar thing.

O2 is going up, the DOC is way down, NH4 is down..time to send out the spores and wait. The main pest algae dies off producing those spores. Plants do better. We can look at all these things, but it really centers on growing good healthy plants.

Algae really are not an issue unless the plants are not growing well, aquatic plants leach all sorts of stuff and they do it differently if they are stressed than they do if they are healthy. 

This also explains why large water changes can mitigate algae under poor conditions for plants and also why adding activated carbon to a healthy plant tank to remove allelopathic chemicals does NOT induce algae blooms.

Ponder those apples


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## Zapins (Jan 7, 2006)

plantbrain said:


> So why don't ADA AS tanks kill plants when newly started up aquariums have higher ppm's of NH4? I was only able to induce Green Water.


Not all batches of aquasoil leach huge amounts of ammonia, but many do. It is a common problem see the following threads as a few of many examples:
http://www.plantedtank.net/forums/showthread.php?t=532554

http://www.plantedtank.net/forums/showthread.php?t=698809

http://www.badmanstropicalfish.com/forum/index.php?topic=30599.0



plantbrain said:


> I'd say herbivores and algae eaters do a lot of the cleaning of aquatic plants in FW and marine seagrass beds. In Florida, most all the nicer rich CO2 springs had loads of snails, Billions of them. There's an old diagram of sunfish that eat snails/zooplankton and bass that eat sunfish, in planted systems where after adding the bass, the water starts to get nice and clean and the populations of the snails and zooplankton shoot way up, and the sun fish populations drops. Classic top down control. Do not discount algae eaters.
> 
> Carpenter's paper/s are the basic reading for these types of ecological concepts. Cited 866 times, might be a good paper to read.
> 
> http://www3.nd.edu/~underc/east/publications/documents/CarpenterandLodge1986.pdf


I don't doubt that animals play some role in algae removal but most people do not keep high enough concentrations of them to be responsible for removing all the algae that could grow if conditions shifted in algae's favor and plants became unable to compete with them.



plantbrain said:


> This also explains why large water changes can mitigate algae under poor conditions for plants and also why adding activated carbon to a healthy plant tank to remove allelopathic chemicals does NOT induce algae blooms.


Yes, water changes can help promote plant growth, especially in situations where ammonia builds up too high. Who is claiming allelopathy is the only reason algae doesn't appear in our tanks?



plantbrain said:


> Ponder those apples


?

Bump:


plantbrain said:


> Aquarist also do not realize or know that their plants are not optimal or limited many times. So increased DOC+NH4+ lower O2 all correlate with poor plant growth. Many aquatic plants tend to respond by auto fragmentation/leaf loss to poor conditions or changes. This reduces any sinks of for resources and sends the fragments out in hopes of finding a better location to grow. Algae do a similar thing.
> 
> O2 is going up, the DOC is way down, NH4 is down..time to send out the spores and wait. The main pest algae dies off producing those spores. Plants do better. We can look at all these things, but it really centers on growing good healthy plants.
> 
> ...


This is exactly the same point I made in my post.


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## kidgrave (Feb 4, 2014)

Zapins said:


> I agree with your points. I think deficiencies and toxicities, allelopathy, shading, etc are the dominant algae controlling factors in planted tanks.
> 
> Here is what I believe causes algae outlined in an organized way (a bit of a long thread to be sure). Let me know what you think.
> http://www.plantedtank.net/forums/showthread.php?t=679601
> ...


If ammonia damages plants, how come people like Takashi Amano and others who use AquaSoil get away with ammonia when they first settle their tanks? ADA Aquasoil releases ammonia for quite a bit.

Bump: I just realized that some of my questions were answered. Thanks for the input guys.


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## Zapins (Jan 7, 2006)

As I said in my post, ammonia is not always released from aquasoil when it is first used. There are "bad batches" of aquasoil that release a lot of it for a few weeks in the beginning of use. The ammonia levels can be reduced by frequent large water changes until the substrate is depleted of ammonia. 

Ammonia is very widely known for damaging certain species of plants when used as the sole source of nitrogen (or when it is overwhelmingly the only source of nitrogen). There are hundreds of papers on the subject. Also, since aquatic plants lack many of the protective features of terrestrial plants (namely the wax cuticle that prevents drying out) they are more susceptible to ammonia burns than terrestrial plants which is why low concentrations of ammonia 1-2 ppm can cause serious harm. HC and UG are particularly sensitive to ammonia burns from what I've seen in various posts.


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## kidgrave (Feb 4, 2014)

Zapins said:


> As I said in my post, ammonia is not always released from aquasoil when it is first used. There are "bad batches" of aquasoil that release a lot of it for a few weeks in the beginning of use. The ammonia levels can be reduced by frequent large water changes until the substrate is depleted of ammonia.
> 
> Ammonia is very widely known for damaging certain species of plants when used as the sole source of nitrogen (or when it is overwhelmingly the only source of nitrogen). There are hundreds of papers on the subject. Also, since aquatic plants lack many of the protective features of terrestrial plants (namely the wax cuticle that prevents drying out) they are more susceptible to ammonia burns than terrestrial plants which is why low concentrations of ammonia 1-2 ppm can cause serious harm. HC and UG are particularly sensitive to ammonia burns from what I've seen in various posts.


Thank you Zapins for answering my question. Also, tank you plantbrain, and everyone else who contributed to answering my question. I hate algae, and can't wait to receive my measuring teaspoons on the mail so that I may start dosing EI and not worry about algae, or plants being defficient.


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## klibs (May 1, 2014)

For me I find that I only get algae when I slack off on taking care of my tank. I won't get into all the scientific reasons but if you have stressed / decaying leaves in the tank algae is soon to follow from what I have seen. Decaying plant mass turns into NH4 so I see how the correlation can be made.

The first thing I do when I start to get new algae is clean my whole tank / filters. usually does the trick. Trim any struggling parts of my plants etc. Usually i don't trim when I should and things become shaded and the lack of light causes decay.

Like Tom says - it really is the case that if you focus on healthy plants and give them optimal conditions then algae will not have a chance.

Just my $0.02


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## kidgrave (Feb 4, 2014)

fablau said:


> I think what Tom said above is key. After several years of planted aquarium keeping, I also agree on the fact that stable systems favorite plants growth whereas unstable systems favorite algae. It is compelling though how plant and algae growth are inversely proportional with each other. When plants thrive, algae struggle and vice versa.
> 
> Fertilizers? Over fertilizing? Not a problem if plants thrive... But if plants struggle, they may contribute to algae growth.
> 
> ...


This is one of the best explanations that I have read online, and it makes a lot of sense to me. I was getting green spot algae in my fish tank. I was dosing PPS Pro, and I still was unable to get rid of it. I guess that it wasn't providing enough nutrients. I started dosing Estimative Index, and now I don't have to worry about algae because my plants are not lacking nutrients.


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## plantbrain (Dec 15, 2003)

kidgrave said:


> This is one of the best explanations that I have read online, and it makes a lot of sense to me. I was getting green spot algae in my fish tank. I was dosing PPS Pro, and I still was unable to get rid of it. I guess that it wasn't providing enough nutrients. I started dosing Estimative Index, and now I don't have to worry about algae because my plants are not lacking nutrients.


This is not quite correct logic, as the methods themselves were not the specific reason for the GSA, more, the lower PO4 recommendation for PPS was more at issue. Adding more PO4 to the mix would/should resolve that issue, but you may be low on other nutrients, particularly with more stems, few fish/feeding fish, higher light etc. 

At low light, or say with Excel dosing only, then it's fine.


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## kidgrave (Feb 4, 2014)

Plant brain, I was dosing 3 times the amount of pps pro, and I was still dealing with algae. I do have a lot of stem plants. Even thoughts it's possible that my plants were deficient of other nutrients, some of my plant leaves were clearly pointing out to phosphate deficiency. Some of their leaf color was turning excessively dark green.


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## Zapins (Jan 7, 2006)

Phosphate deficiency is relatively rare in aquatic plants. Darkened leaves are not the best indicator of phosphorous deficiency either.


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## kidgrave (Feb 4, 2014)

Zapins said:


> Phosphate deficiency is relatively rare in aquatic plants. Darkened leaves are not the best indicator of phosphorous deficiency either.


Part of my Java Fern, Ludwigia repens, and christmas moss leaves were looking abnormally too dark green. The fact that I was dealing with green spot algae points out that I could have been dealing with phosphate deficiency, but it also possible that I may have been dealing with my plants lacking other nutrients, but it is a bit unlikely since did dirt my tank not too long ago. Also, leaves of my ludwigia repens were falling off. 

I searched for similar charts like the ones below, and they all point out to the same issue that I identified. 

http://www.growrealfood.com/gardening/identifying-plant-nutrient-deficiencies/


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## happi (Dec 18, 2009)

this tank gets unlimited fertilizer from both PO4 and NH4/KNO3, 1ppm No3 and 0.7 ppm NH4 from Urea daily. Nh4 from urea work better and safer compare to Nh4no3 IME, ammonia can burn plants when water is hard and PH is high, I have noticed plant will start to melt when ammonia was between 1-2ppm and when I had hard water. 

I have dosed up to 1ppm of Nh4 from urea daily and there were no algae, I dosed Nh4no3 around 0.25ppm and some GDA occurs, so you can see how different source of NH4 also play an important role, every time I dosed excess KNO3 GDA also occur for whatever reason while most plant grew fine. 

Algae can grow in Pure water where there is no nutrients at all, algae require very minimum amount of nutrients to grow as mentioned by Tom Barr. I remember reading an article somewhere how plant growth block the algae from growing but I will have to find that for you, I don't remember much about it.


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## happi (Dec 18, 2009)

kidgrave said:


> Plant brain, I was dosing 3 times the amount of pps pro, and I was still dealing with algae. I do have a lot of stem plants. Even thoughts it's possible that my plants were deficient of other nutrients, some of my plant leaves were clearly pointing out to phosphate deficiency. Some of their leaf color was turning excessively dark green.


 plant will start loosing there reds when NO3 start to rise and they will appear green to dark green, Tom Barr will try to prove me wrong here but you can test this by yourself, make sure you select those plants that are not naturally red and can become red, I was able to turn blyxica japonica red by cold water and minimum NO3, same plant will remain green in high NO3, Ludwigia panantal will remain red even in high NO3. 

here is a picture of tank dosed with EI, most plants are green instead of red.


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## Zapins (Jan 7, 2006)

happi said:


> I remember reading an article somewhere how plant growth block the algae from growing but I will have to find that for you, I don't remember much about it.


This article?
http://www.plantedtank.net/forums/showthread.php?t=679601


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## happi (Dec 18, 2009)

Zapins said:


> This article?
> http://www.plantedtank.net/forums/showthread.php?t=679601


 sorry zapins that's not it, I think Niko showed it to me once, I will ask him.


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## Okedokey (Sep 2, 2014)

its called primary ecological succession (dynamics).

edit, to the other questions regarding red plants, it is a known fact that nitrogen and ferredoxins in plants are indirectly proportional, so i believe that yes, nitrate concentration (starvation particularly) can induce more 'redness'.


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## BigJay (Jun 30, 2009)

plantbrain said:


> Algae spores germinate based on evolutionary cues, this may or may NOT have anything to do with ferts/access. Algae tend to be well adapted for seasonal changes and changes in general. Submersed Aquatic plants tend to be better in more stable systems. Plants need a lot more nutrients than algae to grow. 10-1000X more.


I have a rated question: is one of these evolutionary cues the lack of available CO2? 

Once CO2 is depleted in an environment, (many) plants will start eating into available bicarbonates. It takes energy to do so, and algae is more effective than most plants at using bicarbonates (Walstad'a book - carbon section).

So maybe the lack of CO2 is the cue for spores to germinate, because they have a competitive edge? This may also explain why adding CO2 helps fight algae?

I'm a math and physics guy, not a botanist.


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## Zapins (Jan 7, 2006)

CO2 helps suppress algae because it makes plants grow faster and supports a larger biomass per area than non-injected tanks can support. This means you have a larger amount of plant suppression acting on algae in a given area than non-injected tanks.

There is nothing especially phytotoxic about CO2 that would suppress or harm algae and not plants. Algae use CO2 to grow just like plants do.


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