Cyno/browinish red algae

[innercirclepro]

I have posted about this before but on my sand (not deep sand bed just enough to cover bare bottom) I am getting a few small patches of a film/hair of red/purple/brownish algae. when i see it like that I try and scoop it out but other then that I just run phosguard and do my water changes

I have a 90 gallon with 6 fish and a few corals. My photoperiod is 10 hours. actinics for ten and the 1000k for 6 hours.
nitrate-0
nitrite-0
phosphate-0 ( i know it oculd read zero and still have them, maybe being used up by the algae but my alage isnt that bad i dont beleive)
calcium- 460
alkalinity 170

what can i do to get rid of this?

also on top of my sand it looks like its hard almost like a film. this oculd have been to attributed to the alk and calcium being out of wack over the last few weeks.. but not sure if it has to do wit the algae. i can post a pic if needed.
to anyone who red my last post about the alage the red algae on my rocks went away i only get it in the sand now in small patches. thanks

[sasquatch]

you need to test mag, very hard to get correct ionic balance without, what are you feeding? any other additives/