# Why add fertilisers and additional plants to combat algae?



## Geraint Anderson (21 Oct 2019)

Hi,

I've had my tank set up almost a month and am looking to start adding fertilisers which I'm probably going to use the Estimative Index. But there seems to be conflicting information about the nutrients in the tank, so I think I'm missing something.

On the one hand, all the information seems to say we need lots of plants to use up all the nutrients to combat algae. The Tropica website and numerous posts here recommends adding fast growing plants which will absorb the nutrients from the water column so there's none left for the algae.

On the other hand, the EI dosing adds nutrients in excess at a level that will never be depleted. This article says that algae is caused by nutrient deficiencies.

What am I not understanding?

Thanks,

Geraint


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## Zeus. (22 Oct 2019)

Algae will grow with nutrients in the parts per billion range so having them in excess or lean makes little difference to them.
The reason lots of plants are advised is the plants mop up the light so less light for the algae, fast growers fill tank up quick so mop up light faster, plus their fast growth doesn't give time for the algae to get establish on their leaves.
Excess ferts also means healthy plants so less decaying plants so less toxins, algae likes these toxins


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## dw1305 (22 Oct 2019)

Hi all,





Geraint Anderson said:


> But there seems to be conflicting information about the nutrients in the tank, so I think I'm missing something.


No I think you are right, there is a difference between those who practice some form of nutrient depletion and those who favour non-limiting nutrient levels.

I'm not an EI user, but many people use it, and follow the the EI rules concerning CO2 distribution, flow and water changes to <"stunning effect">. Personally I use the <"Duckweed Index">, a simple technique of observing the colour and growth of a floating plant, as an indication of when to add fertilisers. 





Geraint Anderson said:


> On the one hand, all the information seems to say we need lots of plants to use up all the nutrients to combat algae. The Tropica website and numerous posts here recommends adding fast growing plants which will absorb the nutrients from the water column so there's none left for the algae.


 We don't know exactly why <"having a large plant mass reduces algae">, but it looks pretty conclusive that it does. It doesn't really matter how you get there.

The way I look at it is there are plants we want: "plants", and plants we don't want: "algae", but they are all plants and have the same basic physiological requirements. This is particularly true of the green algae, they belong to the <"same clade"> as all the mosses, ferns and higher plants and have the same photosynthetic pigments etc. In the same way there are photosynthetic organisms which need <"eutrophic, and others that grow in oligotrophic">, conditions in both plants and <"algae">. 

cheers Darrel


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## Tim Harrison (22 Oct 2019)

Algae seem to thrive in environments rich in organics; the remains of decomposed plants and critter waste.

Typically, there will be a high organic load at start up as the system and plants adjust, so it's always best to plant heavily from the get go. Or float fast growing stems to absorb the organics and therefore prevent algae. Dense planting also probably helps prevent algae through a range of other synergistic interactions, such as mutual shading, and allelopathy.

Eutrophic dosing methods like EI use inorganic nutrients which are more readily available to plants than organic nutrients. This probably gives higher plants the competitive edge over algae, especially in a high-energy setup. Starving higher plants of inorganic nutrients will cause decomposition, higher organic load, and algae; hungry plants leak organics and attract algae. That's why it's best to overdose on inorganic nutrients, to ensure the plants are properly fed.

The basic guidelines of EI were never meant to be stuck to rigidly, but are rather a starting point, from which the doses can be tweaked to suit the rate of plant growth. However, if you're just starting out it's best to stick to the original guidelines. That way you have more wriggle room when it comes to making mistakes and therefore a greater chance of succeeding.


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## jaypeecee (24 Oct 2019)

Zeus. said:


> Excess ferts also means healthy plants so less decaying plants so less toxins, algae likes these toxins



Hi Zeus,

To which 'toxins' are you referring?

JPC


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## Zeus. (24 Oct 2019)

The breakdown products from plants failing to thrive due to insufficient ferts to cope with environment factors like high light.
Plants get pinholes if not enough CO2, other elements can cause weak plant structure, malformed leaves, leaves melt and release organic compounds which dissolve in the water  aka toxins which algae appears to thrive on.
Well that's my basic understanding of what happens from my reading around, as to which DOC ( Dissolved Organic Compounds) they actual are I dunno @dw1305 is more more the expert, however I dont think we need to know their complex names just an understanding of what going on is enough IMO


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## dw1305 (24 Oct 2019)

Hi all,





Zeus. said:


> Plants get pinholes if not enough CO2, other elements can cause weak plant structure, malformed leaves, leaves melt and release organic compounds which dissolve in the water aka toxins which algae appears to thrive on.


I think that is it. Plants are carbon based and if they are unhealthy and start shedding leaves etc. then that carbon becomes available and provides a substrate for microbial action. 

cheers Darrel


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## tiger15 (25 Oct 2019)

Zeus. said:


> The breakdown products from plants failing to thrive due to insufficient ferts to cope with environment factors like high light.
> Plants get pinholes if not enough CO2, other elements can cause weak plant structure, malformed leaves, leaves melt and release organic compounds which dissolve in the water  aka toxins which algae appears to thrive on.
> Well that's my basic understanding of what happens from my reading around, as to which DOC ( Dissolved Organic Compounds) they actual are I dunno @dw1305 is more more the expert, however I dont think we need to know their complex names just an understanding of what going on is enough IMO


My planted tank has high DOC loading as I keep a crowded population of cichlid, but no algae.  I struggled initially with algae but once it balances out, algae disappeared.  So I don’t think there is a direct correlation between DOC level and algae as in my case DOC is never minimal as it is steadily added to the system by heavy feeding.  I don’t follow EI or any regiment dosing, just add macros and micros after weekly large WC.  My observation is that when my plants are happy and well fed with nutrients, CO2 and light, algae goes away.  Even though I described balancing as the term is commonly used by aquarists, I don’t know what balancing really means.


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## dw1305 (26 Oct 2019)

Hi all, 





tiger15 said:


> My observation is that when my plants are happy and well fed with nutrients, CO2 and light, algae goes away. Even though I described balancing as the term is commonly used by aquarists, I don’t know what balancing really means.


I think that is quite a good summary.

Healthy plant growth reduces algae, but we don't know why.

As a tank grows in it becomes more stable (again we can't define balanced or stable) and algae declines, but we don't know why.

This occurs over a range of nutrient loadings, so it looks like it is plant growth and time that make the difference, but we don't know why.

cheers Darrel


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## Geraint Anderson (26 Oct 2019)

Thanks. There's so much to learn vs just sticking fish in a tank with some plastic plants. But it's really interesting and I'm glad I found this forum in time and went down this path.

I've just ordered the EI starter kit so I will give that a go. Given that I have a low tech tank at the moment (but might change that after the responses here) I'm probably going to use the duckweed index instead. Do I just add an EI amount of dose but only when the floating plants are looking deficient, or do I continue to dose regularly as I would with EI but the floating plants let me see if I'm getting it right?


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## dw1305 (26 Oct 2019)

Hi all, 





Geraint Anderson said:


> I'm probably going to use the duckweed index instead. Do I just add an EI amount of dose but only when the floating plants are looking deficient? or do I continue to dose regularly as I would with EI but the floating plants let me see if I'm getting it right?


You can do either. if you add a regular dose of fertiliser you won't need the full EI dosage, and I might start with 1/4 of EI.

At the moment I'm using a sort of hybrid "duckweed index", where I add small doses of "Epsom Salts" (MgSO4.7H2O) and FeEDTA regularly, but only add a complete fertiliser when the Frogbit (_Limnobium laevigatum_) <"leaves pale"> and growth has slowed. The reason for this is that if you have <"iron deficiency"> it takes a while for new leaves to grow (iron isn't mobile within the plant) and the <"fertiliser I've been using"> has a low magnesium content.

cheers Darrel


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