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Cyanobacteria in plant-only grow-out tank

1386 Views 3 Replies 3 Participants Last post by  iceburg
I have a 10 gallon tank that I've been using as a high-light, high-CO2 grow out tank. Aside from some tiny pest snails it currently has no animals. Unfortunately it's developing some cyanobacteria colonies on the ADA Aquasoil substrate. I'm guessing insufficient aeration probably contributed to the growth so I'm increasing that even if it does "waste" a bit more CO2. I also haven't been very diligent with water changes in this tank since there are no animals but that can be improved going forward..

Now, the challenge is getting rid of what's already there. I tried spot treating with H2O2 but the bubbles lifted up smaller soil particles with the cyanobacteria and spread them all over the tank. :eek: Since there are no livestock and I'm not too concerned with preserving the cycle I'm looking for an aggressive cyanobacteria treatment that is still plant safe. I know erythromycin can do it, but are there any other plant-safe options for killing cyanobacteria?

P.S. Killing the pest snails as well while remaining safe for future inverts down the road would be a bonus.
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if you have truly BGA (cyanobacteria) and not a form of bluish green looking algae, then Erythromycin (or a derivative thereof like Azithromycin) is by far your best option. One dose of 200 mg per 20 gal will get rid of BGA once-and-for-all.

However, you have to be careful with handling your tank. BGA is everywhere and it can be re-introduced into your tank readily.

Good luck.
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g4 is certainly right in that chemical warfare with erythro will kill the BGA but it's just gonna come back if you don't solve the root cause.

do you have any flow in your growout tank? if it is just stagnant water then this comes as no surprise... while bio filtration is not necessary some mechanical filtration certainly wouldn't hurt and flow is absolutely necessary to prevent waste buildup in areas and distribute nutrients etc...

one of the most common reasons for BGA appearing is lack of water movement in a particular area. waste buildup in spots are where BGA thrives. BGA also hates oxygen I believe so water movement helps take care of that issue as well.

Also pics would help...

I also disagree that BGA needs to be 'introduced' to get it. While it is indeed a bacteria IMO it is always present to some degree within our tanks and it will show up when the conditions favor its growth.

I could take a patch of BGA and drop it in a well balanced tank and it will die off on its own. It will only thrive if you let it.
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Thanks for the replies. It looked like my earlier H2O2 attempts may have paid off at eliminating the visible colonies after all, but I'll still need to address the root cause to keep it from coming back.
@g4search: It's possible that it's something else, but it looked a lot like the photos I've seen of BGA outbreaks. I'll get some Erythromycin to keep on hand if it starts coming back.
@klibs. My tank has mild circulation from an old, small air driven filter that has probably become far less effective as the plant density increased. I initially started with a HOB filter with only mechanical media but the downward flow from the hob was too much for the 10g tank and was stirring up the aquasoil so I switched to the bubble driven. The BGA did mainly colonized an area along one edge of the tank that was probably blocked from circulation by plants. I'll see if I can rig up a guard to let me use the HOB without disturbing the soil

Thanks again.
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