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Is this algae?

matthew xia

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Hi - Can anyone tell me what this is growing on what I think is Hornwort... The patches of white/blue around the leaves (where they grow off the central stem) arrived recently and I wondered if it was a danger to the tank?
IMG_1592.jpg
 

Byron

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It looks like cyanobacteria to me too. This is often assumed to be an algae but it is actually a bacteria. It is caused by organics in the presence of light. If allowed to go unchecked, it will in time literally smother the entire biological system of the aquarium.

Organics are kept under control by not overstocking, not overfeeding, regular substantial water changes, vacuuming the substrate (in open areas), and keeping the filter well cleaned. Any brownish gunk you find is organics.
 

Byron

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Is this not a bit unusual as there hasn't been anything in the tank except the cycle....?
No. Cyanobacteria can appear anywhere where there are organics and strong light. You might be surprised at how many organics are dissolved in ordinary tap water. The bacterial bloom common in new tanks for example is solely due to the large organic presence in tap water which feeds the rapidly-multiplying bacteria that feed on organics (different from nitrifying bacteria).

You might reduce the light and see if it helps. Floating plants can help with this too. I have had this work in tanks that were close to a window and developed cyanobacteria.
 
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