Dark algae

[MikeyC]

Hi everyone.

I've upgraded my tank from 30l to 120l and have recently started to get outbreaks of a black/dark purple algae around the bottom of the tank.
I had a water test done at my lf whi said there was nothing shoeing that would cause it (if anything phosphate and nitrate was a bit low). They recommended increasing the flow so I installed a 2000l/h wave maker which has increased the flow but the algae keeps coming back.
Any help/advice would be great as I don't want my frags to get killed off by it!

 

[HankstankXXXL750]

You should get a microscope and see if it is dinoflagellates. Low nitrate and Phosphates can lead to this I e been told.