Help with black algae plz

[maudsley]

hi guys can anyone help me,

i have tested water and all results are perfect but
i have started getting this black hair like algae all over my plants and its started on the rocks, wood and filteration pipes aswell. so this wk end just gone i totally stripped all wood rocks out, binned all plants as i can not clean the algae off them without damage. hoovered all gravel. the re planted tank with new plants and re decorated. i have fears that this algae will come back though. my set up is,

55gallon/190ltrs corner unit
fluval 305 external filter
x2 T5 lights on for 7 hrs a day
undergravel fertilizer for plants
rocks, bogwood
6 red belly piranhas

 

[LowCel]

How old are your bulbs? Replacing my bulbs did more to get rid of mine than anything else. I also did a lot of water changes and replaced the bulb in my UV sterilizer.

 

[Citrinellus]

How big are you rbps? ^ i agree, I would get a uv or upgrade to uv sterilizer.

 

[maudsley]

they are about 3". the tank was brand new around december time so bulbs are new