purple up is junk I would never recommend adding any type of additives to a new tank or any tank for that matter they only cause problems , leave that to the more experienced .
from what I see its cayno Large water changes will help , I don't see any power heads in your tank , power heads in a salt water tank are a must for circulation ,
no circulation is like having stagnant water sitting one big dead spot . this is what causes cayno to sit on your rocks and sand , cayno is caused by the silicates being released from the sand in your tank , having power heads will help circulate your water not allowing those dead spots where this nasty looking algae forms ,
cayno is normal in new tanks so don't be alarmed with it , like I said good circulation and large water changes will help get you through this phase ,
with saltwater good circulation and water changes are your friend , there is no need to add any type of additives to your tank everything you need is in your salt , your rock will color up over time , the only time you would need to start adding any type of additives is when your heavily stocked with coral mainly sps
, but still use caution .
additives can lead to many issues that could have been prevented if you never used them , only the more experienced reefers use them as they learned how they react with one another . not knowing what can be added with what can cause big issues even crash a tank.
I've been keeping reefs for many years I still am Leary of using additives , water changes keep my tanks healthy and clean ,
baby steps with saltwater learn as you go , never rush into things your not sure about research ask a lot of questions first , always be sure your comfortable with your trying to do , many times thing can't be reversed and bad things can happen to both coral and fish.