Sudden Onset Of Possible Hair Algae & Black Beard Algae..

[Harlequins]

I noticed in my tank,its suddenly developed what looks like fine stranded hair algae,which tends to be around the spraybars and black beard algae growing on my artificial ornaments.
The tank regulary gets a 30% weekly w/c and sand clean.
The 55 gal tank has been set up for over a year and has been running perfectly with only slight algae on the glass,which gets cleaned weekly.
It has 2 tetratec externals running on it,with the spraybars running across the surface from back to front.
Ammonia/nitrite 0 nitrate 20(tap 10)ph 7.8-8.
The only real plant in there appears to be thriving and has runners coming up through the sand.
No new additions at all,the only thing i've done recently is clean the filter tubes through...hence flow is back to full force...
Twin bar lights which are normally on for maybe 2 hours in the morning,less if i'm at work and around 3-4 hours in the evening.

Can anyone shed any light on this please,seems strange its starting all of a sudden.
I keep the tank clean and don't overfeed,so why?

Any help to stop this spreading would be great

Thanks

 

[SuperColey1]

The only real plant in there appears to be thriving and has runners coming up through the sand.

1 plant is not going to follow 'planted' principles. This is is essentially a non planted tank.

black beard algae growing on my artificial ornaments.

Pretty normal IME for a non planted tank.

Twin bar lights

What wattage and the tank size is?

Basically for a tank with one plant in it there isn't much we can say really. If this is a problem that hasn't reared it's head for a whole year and then suddenly appeared then there is obviously a change of some sort in the tank. Any new additions? Change in fish foods? Change in routine?

May well be just a slight change in the tap water parameters for a week or too, hopefully not permanent, which has 'triggered' the algae.

AC