How to get rid of BGA

[Genirous]

Hello from Athens!
I have a serious problem with BGA in my tank...
I have tried a 3-day complete blackout twice, but without solving the problem...
I have read a lot about why BGA is formed, opinions like poor water quality, poor water circulation, poor nitrates, lots of nutrients, lots of light, lots of phosphates etc
I didn't come up to a conclusion though...
So, I need your opinion in this...my water parametres are:
pH: 7.2
kH: 6
GH: 10
NO2: 0
NO3: ~0
NH3/NH4: 0
PO4: ~2

Internal filter 1500 litres/hour
Lighting 4x36W
No fertilisation except JBL Aquabasis substrate
Plants: 5 echinodorous bleheri

[Drumachine09]

How big is the tank, and are you doing Co2?

[dev]

Hello from Athens!
I have a serious problem with BGA in my tank...
I have tried a 3-day complete blackout twice, but without solving the problem...


I reccomend a 5-7 day complete blackout. No food, no water change, no light. You need to cover up the aquarium with sometething like a blanket. Depending on your stock, there may be reasons not to do this.

For very small areas with cyano-bacteria in a larger tank, local concentrations of salt may be used, and will kill the bacteria almost immediately. You will see them start turning red after only a few minutes, and after a couple of hours they will have dissolved completely. This must be done with great care, and is not reccomended if you have any fish or plants that have a sensitivity to salt.

A broad spectrum antibiotic, like Tetra General Tonic will also help remove the BGA/cyano.

As for the reason, the reasons you have found sounds about right. I usually see them in areas with low circulation and some localized decomposition and limited supply of nitrogen, like between some rotting leaves. If they attack the entire tank you have a more general problem.

I think your nitrates are too low. Consider adding some through KNO3 or CaNO3. I also think your phosphate level is a little high, I would try to keep it below 1 ppm. You should also consider adding a fertilizer that contains the required trace elements but not phosphates or nitrates.

[Genirous]

Drumachine09 my tank (with the problem) is 400 litres and no I don't have CO2...
dev the areas with cyano-bacteria unfortunately are not small...
As for your proposals, I surely prefer the 5-7 day blackout, but I am afraid that it won't solve the problem...
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I would like to ask for your opinions about the Redfield ratio!
Is it the solution to algae problems, what do you think..?
And if it is, should I only zero my phosphates or follow dev's proposal...?
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[Drumachine09]

well, 400 liters is what, 110 gallons? i dont thiink you are over doseing on lights, so, mybe hungry hound can help.

[dev]

As for your proposals, I surely prefer the 5-7 day blackout, but I am afraid that it won't solve the problem...

You are right, it will not solve your problem - it will completely kill the cyanobacteria, but if the original problem is not solved, they will return at one point or the other.

That's a very interesting table. While I'm not familiar with the Redfield ratio, it does show how high nitrates will prevent growth of cyanobacteria, while too high levels will promote algae growth. In my experience KNO3 is more effective at preventing BGA than CaNO3.

In my planted tanks I try to keep the phosphates a little less than 1 ppm and the nitrates in the range 10-20 ppm.

In other words, I would do both - make sure your phosphate and nitrate levels are good, that you have no ammonia or nitrites, that your water has enough oxygen and that your filtering and water changing routine is good enough. Then kill the cyanobacteria using either the traditional method of blackout (3 days may not be enough, 5 days to a week is better), or by using one of the modern methods such as a handheld UV-light or Hydrogen Peroxide (H2O2). Antibiotics can also be used, but I don't like to reccomend it.

Good luck!

[Drumachine09]

Isnt cyano caused by excess silicates?

[dev]

Isnt cyano caused by excess silicates?

We are now at the border of my knowledge, but I think this is still a bit unclear. While it was believed that silicate depletion could trigger a bloom of cyanobacteria, it is now believed that growth of cyanobacteria can be promoted by higer concentrations of most dissolved organics including silicates. It is also fairly certain that cyanobacteria does not like higher concentrations of nitrogen.

I think silicates is more commonly known to affect diatoms aka brown algae, when the Silicate to Phosphate ratio is high.

[Chrona]

Cyanobacteria can fix nitrogen, which is why they do so well in low nitrate environments. Add nitrates, and the plants/other algae will outcompete them. Excess silicates is usually associated with diatoms or brown algae. Haven't heard anything with regards to cyanobacteria though.