Blue Green Algae, Nutrients and Oxygen

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swozzie

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I have had a planted tank setup for a couple of months now. I have Deponit mixed with silver sand covered with inert gravel for the substrate. CO2 injection keeping the pH 6.8-7.0 and have been following Dennerle instructions and putting in what seems like loads of nutrients for the plants (S7, E15, V30 and pflanzen-gold-7).

Sounds great but the plants grow like mad! Every 2 weeks the tank is overgrown and I have to keep removing plants. I am trying to replace them with slow growing plants and ones that don't shoot out of the top of the tank!

However, now I also a blue-algae problem.

I intend to stop putting in nutrients in the tank and see how the plants go, I suspect they will be fine if they just use the nutrients in the substrate but at the same time I need to get rid of the blue green algae.

I did a 3 day black out in one of my other tanks a while ago and that seems to have done the trick. Just remove as much algae as possible, do a water change, stop putting nutrients in the tank and starve the blue green algae of light for 3 days. However, I am worried that if I do this with my new tank then I will have oxygen problems.

At the end of the day the water is saturated with oxygen (8mg/l +). In the mornings it is like 5mg/l or less. I left the light off for 1 day a while ago and the next day my Red Line Torpedo barbs seemed to be gulping alot. I tested the oxygen content and it was very low (around 2mg/l). If I do a 3 day black out then will the fish suffocate?

What do think is the best course of action

1. 3 day blackout with risk of suffocation? (I could keep doing daily water changes to inject some more oxygen into the water).
2. Try to get hold of some Maracyn (Erythromycin) although that seems to be difficult to come by in the UK
3. Stop adding nutrients and hope the blue green algae goes away
 
Blue Green algae is actually bacterial, cyanobacteria.

Something to try is adding some common Egeria densa plant. This exudes a simple antibiotic which can kill blue green algae. The problem, of course, is that stuff grows like a weed and your conditions sound ideal for it - so you'll need to keep it under control.
 

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