# cyanobacteria



## paleo (7 Sep 2015)

Hi,

I have an old established 350 litre tank, with a fair amount of plants, and not a lot of fish.  Recently, the tank had an outbreak of cyanobacteria, which is quite bad.  The glass get almost completely covered by the stuff in three or four days, as do the plants.

I read on the internet that an outbreak of cyanobacteria can be caused by too little nitrate in the water, but also that it can be caused by too much.  I have been gradually adding more Seachem nitrogen; last week I added 20 ml.  This morning, nitrate readings were still zero, and the cyanobacteria are doing very well..

I would be grateful for some advice.  Has anyone successfully eradicated this pest?  Do products like Blue Exit or ATM outbreak help?

Many thanks,

Paleo.


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## Julian (7 Sep 2015)

Too much light or excessive light duration. Is it near a window..?


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## paleo (7 Sep 2015)

Thanks for the suggestion.

It isn't.  It is in the same place it has been for 20 years, and I never had cyanobacteria before.  The tubes may be getting a bit old, but that has happened before as well.


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## Edvet (7 Sep 2015)

How are the plants doing?  (a three day blackout will clean it up, just do a large waterchange before and after and gove plenty ferts after).


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## dw1305 (7 Sep 2015)

Hi all, 





paleo said:


> It isn't. It is in the same place it has been for 20 years, and I never had cyanobacteria before.


Have you cleaned the filter recently? I only ever get a bit of BGA if the filter needs cleaning.

cheers Darrel


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## paleo (7 Sep 2015)

The plants are growing more slowly than usual.  The duckweed is hardly growing at all!

I just cleaned the filter yesterday.  It wasn't too bad; cleaned it about a month ago.

Thanks for the responses.


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## Martin in Holland (8 Sep 2015)

The flow might be effected somehow (plants obstructing, filter clogged, kinked hose), maybe you got new curtains or just pruned/removed a tree or shrub outside your window which would let more light into the room.
I had great success with spot treating cyno with KNO3 in the past, just the usual dosage in some water direct squirted on the cyno and you can see it bubble away.


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## dw1305 (8 Sep 2015)

Hi all,





paleo said:


> The plants are growing more slowly than usual. The duckweed is hardly growing at all!


Have a look at the <"Duckweed Index">.

cheers Darrel


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## Martin in Holland (8 Sep 2015)

Darrel....couldn't you make a "indication list" for duckweed e.r. leaves getting yellow - add KNO3 and MgSO4 (I'm not sure if that would be right, but you get the idea).


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## dw1305 (9 Sep 2015)

Hi all, 





Martin in China said:


> couldn't you make a "indication list" for duckweed e.r. leaves getting yellow - add KNO3 and MgSO4 (I'm not sure if that would be right, but you get the idea).


 There is work actually on Duckweed _(Lemna minor_) (because of its use in <"ecotoxicology">), have a look at <"Biological test methods.....">,  but  I don't know of any specifically for _Limnobium laevigatum_ etc.

If we make the assumption that the plant is receiving sufficient PAR, it would be possible to produce deficiency symptoms in culture. The problem is that it is quite time consuming, and you need analytical grade salts (to avoid impurities) to make up the solutions, and you would need some more unusual salts to create solutions lacking chlorine (Cl), sulphur (S) etc. You also need a minimum of six replicates of each culture, for statistical purposes, an initial single cloned plant (to remove genetic effects) and standard growing conditions.

The other problem is that  there are 14 separate elements essential for plant growth, but in very differing amounts. If you ignore the three gases - carbon(C), hydrogen(H) and oxygen(O) they are:

Macro
*N, K*, *P
"Secondary macro", 
Mg*, Ca, S
*Micro,*
B, Cl, Co, Cu, *Fe*, Mn, Mo, Zn

Because of this, I used a mixture of likelihood, and <"whether an element is mobile within the plant">, to  diagnose deficiencies.  I should start with the disclaimer that all the tanks I have are low in all nutrients (deduced from the low conductivity ~ 100 microS) and have soft water. I initially stopped using _Lemna_ as my "Duckweed" because it never looked happy in the tanks, even when other plants were still in active growth. _Vallisneria_ is another plant that grows well in our tap water, (hard but low in nutrients), but doesn't survive in the tanks.

By using a floating plant, with access to aerial CO2 levels, that took both light (PAR) and CO2 out of the equation.

This leaves the three macro-elements as the most likely sources of deficiency (because plants need most of them), and plants actually need a lot more N and K than they do P. Nitrogen, P and K are all mobile within the plant, meaning deficiency symptoms will effect older leaves.

We can differentiate between acute P and  N & K deficiencies by symptom. Phosphorus deficiency causes older leaves to show purple overtones, and new leaves to be very small. Nitrogen and potassium deficiencies cause new leaves to be small and older leaves to *yellow.*
I've never had obvious acute phosphorus deficiency, although this may relate to specifically to _Limnobium, _and if you look at the photos in <"Low maintenance..."> that may be P deficiency around the edges of the older leaves on the larger plant.






Yellow older leaves, and a lack of vigour I get a lot, and  usually these can be rapidly greened by the addition of KNO3. As this supplies both nitrogen and potassium I don't know which is the limiting element, and both are mobile within the plant. If your plants show darker leaf veins (interveinal chlorisis)*, that would suggest potassium.  Otherwise nitrogen is most likely.



 *

The other possibility for interveinal chlorosis on older leaves is magnesium (Mg), plants need much less of this than they do N or K, but high levels of Ca (calcium), and to some degree K, effect uptake. *If you have hard water magnesium is a much more likely deficiency*. 

The final element that I've seen deficiency symptoms of is iron (Fe), this is non-mobile so effects newer leaves. I have one tank where the _Limnobium_ never looks very happy, was always being eaten by the snails and it didn't perk up after the addition of KNO3 or MgSO4.7H2O. I eventually resorted to occasionally replacing the ailing Frogbit with healthier plants from the adjoining tank. These would then start the same slow decline. Looked at in the cold light of day iron deficiency was always a likely cause, but I was resistant to this as an idea. The only real difference from the other tanks is that this tank has a very thin layer of silica sand as a substrate and it is always mulm free. As soon as I added some FeEDTA, the plants greened.

Again *iron deficiencies are much more likely in hard water.*

cheers Darrel


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## Martin in Holland (10 Sep 2015)

Cool Darrel...thx...I'm sure this will be very helpful.


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## paleo (10 Sep 2015)

Hi,

Thanks Darrel for your knowledgeable post.  

@Guest: I don't know why nitrate is at 0; one possibility is that the cyanobacteria absorb it all.

I have just added a dose of ATM Outbreak, and will repeat this tomorrow, in an attempt to reduce the organics in the tank.  I will increase the fertilisation gradually, using the Seachem products that I have.

If after that, the cyanobacteria are still doing well, I will do the dark tank manoevre suggested by edvet above.

Please let me know if this course of action is unwise.


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## Edvet (10 Sep 2015)

http://www.theplantedtank.co.uk/algae.htm


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## paleo (11 Sep 2015)

@ Guest: Yes I did.

@ Edvet: Thanks for the link.  Do you have any ideas as to why there would suddenly be a flare-up of cyanobacteria?  The T5 tubes may be getting old.  Also, due to a technical glitch, CO2 injection was interupted for a few days. Shortly after that, the bacteria struck.  I will do the dark tank thing, but I would like to know why the outbreak happened, so I can prevent it in future.


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## dw1305 (11 Sep 2015)

Hi all,





paleo said:


> The T5 tubes may be getting old


It is unlikely to be the tubes, because T5 tubes are "triphosphate" and electronically ballasted, so they  show very little <"light lumen depreciation"> until they fail. Assuming they are 4' 54W tubes? and you want to change them, they are <"cheap to buy">, and any "daylight" (6500K) tube will do.  





paleo said:


> The plants are growing more slowly than usual. The duckweed is hardly growing at all!


 I don't know about the _Cyanobacteria_, but the plant growth is a nutrient issue. 

You can tell it isn't CO2, because floating plants have access to aerial CO2 (~400ppm). 





paleo said:


> I don't know why nitrate is at 0


 Realistically it could be any value, the problem lies with the kit, monovalent anions like NO3- are really difficult to measure accurately, even with analytical grade scientific equipment. Have a look at <"Will fishless cycling....">, the whole thread is worth a read.

cheers Darrel


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## Edvet (11 Sep 2015)

most logical: CO2 fails -> plants get into trouble -> start leaching nasty's -> algea see their opportunity -> algae proliferate


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## paleo (11 Sep 2015)

@Edvet:thanks, that makes sense.  Got the CO2 sorted now, and am increasing the ferts.

@Darrel: I have 3 80w tubes.  Would 3 cheap 6500k tubes do it, or would you recommend using different tubes with different spectra?


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## Edvet (12 Sep 2015)

paleo said:


> Would 3 cheap 6500k tubes do


perfectly


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