# why fully planted tanks has little algae, a theory



## Akaliman (Jul 28, 2014)

I have been battling algae since the start of this tank. The turning point is when I put duckweed. and 15 bushy-nose pleco. I arrange the duck weed so that only half of the tank is covered.




before I put duckweed and plecos the whole woods is covered by alage (dark color). after about one week, the pleco really did clean it up good


Tom Barr's said that if you make sure the plants thrive, the tank will get rid of algae by it self. BUT WHY?
given the duckweed arrangement above I want to propose a theory:

1. I reject the idea that fully planted tank repels algae because it outcompete algae for lights. because in my case I only cover half of the tank. and the other half part of the tank that is not covered by duckweed on top is also algae free.

2. it is also not because the plant out compete for nutrient, because in this tank I keep nitrate 30ppm, PO4 2ppm, and potassium 30ppm the whole time. there's plenty of nutrient for all the plants and algae

3. it is also not because of a "balanced tank". what is a "balanced tank" anyway? every plants have different requirement. some plants are N hungry, and other K are hungry. they don't absorb NPK at the same ratio. so it is impossible to create a "balanced tank" for all type plants. if there is a such "balanced tank", I would say it has a big range.. something like N:K:micros = 10:10:2:2, where the 10 is actually be 10 to 30. 

4. some people says that healthy growing plants emit toxin that prohibits algae growth. I know that this idea is widely rejected, or at least there is no evidence to support it. but In my opinion, this may be the real explanation.

what do you guys think?


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## al4n (Nov 18, 2008)

take out your duckweed for a month, keep your dosing and feeding routine the same and report back


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## Overwatch (Nov 26, 2016)

Akaliman said:


> I have been battling algae since the start of this tank. The turning point is when I put duckweed. and 15 bushy-nose pleco. I arrange the duck weed so that only half of the tank is covered.
> 
> 
> 
> ...


Why is #4 considered a crazy idea? I read somewhere that plants will release chemicals to communicate information to each other. Like the smell of freshly cut grass is them telling people there is a grass massacre. 

I don't have the equipment but why are there not scientist who can figure this out? 

I would like to know this information as well.


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## Akaliman (Jul 28, 2014)

al4n said:


> take out your duckweed for a month, keep your dosing and feeding routine the same and report back


that's easy, algae will thrive. I won't do that :grin2::grin2:
but eventually I intend to remove all the 95% of the duck weed tho

Bump:


Overwatch said:


> Like the smell of freshly cut grass is them telling people there is a grass massacre.


yes I heard that too. that's an interesting correlation


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## Hoppy (Dec 24, 2005)

The reason the theory that plants release chemicals that repel algae isn't considered to be correct is:
Those chemicals being released will necessarily be large organic molecules. (Simple, small organic and inorganic molecules have been tested and do not repel algae.)
Activated carbon adsorbs large organic molecules very effectively.
When activated carbon is used on algae-free tanks the tanks don't experience big algae attacks. (The activated carbon will have adsorbed the chemicals.)
Therefore, the theory can't be correct.
In addition, the adsorbed chemicals can be separated and analyzed to see what they are, but no such chemicals are found.


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## 691175002 (Apr 28, 2009)

Akaliman said:


> Some people says that healthy growing plants emit toxin that prohibits algae growth. I know that this idea is widely rejected, or at least there is no evidence to support it. but In my opinion, this may be the real explanation.


The concept you describe (Allelopathy) cannot occur because it predicts too many things that are false. If plants emitted a toxin that inhibited algae, chemical filtration or even a waterchange would result in an algae outbreak.


I've been thinking about what causes algae for years, and I think I've come pretty close to a theory that can make useful predictions. The key was observing that algae outbreaks in my bookshelf setup (in which four tanks share the same water with high turnover) would stay localized to a single tank. Overfeeding would only produce algae in a single tank, despite all four sharing water at roughly 30x turnover. This means that any long-run property of the water cannot cause algae. I currently believe that algae responds to fluctuations in DOC or NH4 that are too small and fast to measure. Adding plants (especially floaters) can help immediately absorb any waste, but no amount of plants can offset a poorly maintained aquarium.

I also ran the setup for over a year without any biological filtration (relying only on plants) and had a small and persistent amount of thread algae despite no measurable Ammonia or Nitrites. Adding biomedia to the sump (in preparation for fish) eliminated this problem.

There are also the other obvious causes of algae such as major light/CO2/nutrient imbalances, or just poor water quality.


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## Akaliman (Jul 28, 2014)

@691175002: I'll buy this theory. NH4 is not something that one dose, so this does not contradict my above point #2 & #3. 
I have also red that BBA is by product of too much bioloads (too many fish), in which organic matter (left over fish food and fecal material) is convert to among other things multi vitamins (and NH4 as well).


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## Jeff5614 (Dec 29, 2005)

Akaliman said:


> @691175002: I'll buy this theory. NH4 is not something that one dose, so this does not contradict my above point #2 & #3.
> I have also red that BBA is by product of too much bioloads (too many fish), in which organic matter (left over fish food and fecal material) is convert to among other things multi vitamins (and NH4 as well).


Actually, a lot of commercial liquid ferts such as ADA, Seachem and Tropica contain a small amount of ammonia along with urea and nitrate.


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## BettaBettas (Aug 21, 2016)

I think #4 is a very good idea.. Cedars, and some pines... release chemicals around them to repel plants growing in there perimeter.. why is this? because pines and cedars usually grow in low nutrient soils. so they kill or repel the competitors!
This could happen to submerged plants / aquatic plants to!


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## Akaliman (Jul 28, 2014)

Jeff5614 said:


> Actually, a lot of commercial liquid ferts such as ADA, Seachem and Tropica contain a small amount of ammonia along with urea and nitrate.


so this contradicts to @*691175002*'s idea? 
maybe its not ammonia since @*691175002* weren't able to detect it in his book shelves tank. maybe some other nutrient from organics matter, like multi vitamins?



BettaBettas said:


> I think #4 is a very good idea.. Cedars, and some pines... release chemicals around them to repel plants growing in there perimeter.. why is this? because pines and cedars usually grow in low nutrient soils. so they kill or repel the competitors!
> This could happen to submerged plants / aquatic plants to!


yes many species in both animal and plants kingdom use chemicals. wild almond is one the most famous for Cyanide.

but I am leaning toward @*Hoppy*, that is if #4 is correct , more water changes would make make more algae as the toxin is waste away. 
@*691175002* has the right idea, but it may not ammonia (you said yourself ammonia wasn't detectable, and commercial fertilizer has ammonia) but something that is very vital to algae. something that is catalytic in nature to algae metabolism. 

why catalytic? because without it, algae can still grow, but it would take much more concentrations of reactants (N, P, & K).

I have a nano tank that was fine for months, then one day I overdosed on fertilizer , I was curious to see what happen. I didn't water change. in 48 hours time, i saw all kinds of algae: Green Dust Algae, thread algae, brown algae.


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## Jeff5614 (Dec 29, 2005)

Akaliman said:


> so this contradicts to @*691175002*'s idea?
> maybe its not ammonia since @*691175002* weren't able to detect it in his book shelves tank. maybe some other nutrient from organics matter, like multi vitamins?


I don't know if it's contradictory or not. I was just mentioning that those ferts do contain an ammoniacal source of nitrogen. So if one is using those they're adding ammonia to their tanks, albeit a very small amount, I would think.


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## TwoTurtles (Jul 18, 2016)

Allelopathy is undoubtedly real. See for example Isolation and Characterization of a Novel Antialgal Allelochemical from Phragmites communis as just one of the many articles that come up when you search for it. Incidentally, none of the articles I could see even suggested that there was controversy about it. It has been tested in lab conditions. It's used commercially. It's real. 

Of course there is a big difference between "some plants release algae inhibiting allelochemicals" and "the algae reduction in this case is the result of allelochemicals" which is different again to "Allelopathy is common in aquaria". 

The first is true but the other two are much harder to answer because our tanks are such complex systems that to say any one factor causes or prevents algae is always a simplification.

Regardless of that, I'm glad you have found a method that works and your tank is looking good. I'm currently using water lettuce for the same purpose.


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## Akaliman (Jul 28, 2014)

this is so cool. nice link @TwoTurtles

"Antialgal allelochemicals were isolated from Phragmites communis Tris. The isolated allelopathic fraction showed strong inhibition activity on the growth of Chlorella pyrenoidosa and Microcystis aeruginosa but had no inhibition on Chlorella vulgaris. The 50% effective concentrations (EC50) of the allelopathic fractions on C. pyrenoidosa and M. aeruginosa were 0.49 and 0.79 mg/liter, respectively. The allelopathic activity of the fraction was species-specific. *The isolated allelopathic fraction caused metal ion leakage from algal cells. "*

it is so potent, EC50 of less than 1 PPM


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## Vohlk (Apr 8, 2016)

Out of curiosity, how can you ensure #1, how can you know as to why the algae went away. Was it a result of the duckweed, or the 15 plecos added. (most likely both) But how did each contribute to the reduction in algae, was it the "cover" provided by the duckweed, or the soaking up of excess nutrients, or did they contribute at all and was it just simply the fact that there where 15 hungry plecos? It's hard to tell.

I don't mean to say as to whether #1 is true or not as stated. Just trying to point out possible experimental oversights that is all. It would seem that changing more than 1 variable at a time would not lead to a conclusive result.


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## Akaliman (Jul 28, 2014)

Vohlk said:


> Out of curiosity, how can you ensure #1, how can you know as to why the algae went away. Was it a result of the duckweed, or the 15 plecos added. (most likely both) But how did each contribute to the reduction in algae, was it the "cover" provided by the duckweed, or the soaking up of excess nutrients, or did they contribute at all and was it just simply the fact that there where 15 hungry plecos? It's hard to tell.


totally valid point, I did not isolate into 1 variable only, which is the duckweed.

I didn't mention this, but before the duck weed, BBA is thriving. As far as we know, plecos does not touch BBA. since I put duckweed, BBA is also greatly reduce. 

as far as the question of duck weed "provides cover" or "soaking up the nutrient", it is for sure NOT the cover. because the duckweed only floats in the half part of the tank where the bottom has no plant nor substrate (by design). the other half part where the tank has plants, did not cover by duckweed. 

whether nutrient being soaked up or allelochemical at work is what we trying to find out :grin2:


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## Akaliman (Jul 28, 2014)

here's to better understand the tank situation


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