I have red algae on my rocks in various places, in patches on the fine sand bed and also purple algae on my fine sand bed.
I think I identified the problem to be a home-made plastic mesh to cover my outgoing hose for my filter (since an anenome died after getting stuck on it). I used to get within a day almost the entire sand bed covered in a deep purple algae which I could pick up in large pieces (it broke away if I wasn't gentle). After removing the home-made plastic mesh the algae is probably 85% gone so all I do now is just shift the sand around. I think this has let pieces of the algae go around the tank and it's growing from there still.
I hope that chemi-clean will fix the problem. I purchased this red algae removing solution but I didn't read the label fully before purchase as it was not safe with corals.
Refer to my signature for what I have in my tank. Chemi-clean sounds the best for this problem. Am I correct?