Algae

[frostiex]

Hi all my tank is 33 gal @ about 4 weeks old..last week it started to develop this ugly dark brown / purple algae on my substrates. ( I have crush coral)

I used to have some angel hair algae a piece of my rock...but those have been cleaned up by my snails.

I have changed the water twice so far. on the second week and 3rd week and planning on doing it again tomorrow.

on my last water change I have also added some phosguard to the filter.
but this brownish algae is ugly how do I get rid of it?....an suggestions?