Red Growth ?

[Paddski]

I have a 360 litre Juwel. In the last few weeks this red type of Algae has started growing but only on these red rocks and a little on the bogwood. No live plants.

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[Byron]

That is brush algae, sometimes referred to as beard algae. It can appear in various shades of black/brown, dark green, dark gray, and reddish as here. It is actually a "red" algae by definition, as opposed to other algae which may be green or brown primarily.

This algae is harmless to fish, and actually is beneficial. Like higher plants, it uses nutrients and produces oxygen, though minimally compared to most higher plants. It is a nuisance in planted tanks because there it usually means there is an imbalance in the light/nutrient balance and it can cover plant leaves, suffocating them and killing the plant. Aside from this, it is not harmful. Many (including myself) consider it quite attractive and it is certainly natural-looking. I have it on most of the wood in my tanks, even with live plants, but I control the light/nutrients to prevent it from spreading onto plants.

It can be indicative of too nutrient-rich water, meaning insufficient water changes,overfeeding, over crowding fish, insufficient substrate cleaning or insufficient filter cleaning. Nitrates may rise as another sign of these problems, though one should not use nitrates alone as the basis for good maintenance.

Byron.