I am new to this hobby myself but I learned a very important lesson from a man named "KIP" from this site.
Tap Water is a "NO_NO_NO NO _NO!!!!!! I started my tank over 3 monts ago and I used tap water that sat for 2 days (55g)
I went through the normal stages but could never get rid of the brown algea, UNTIL "KIP" answerd my post. He told me "NO!!" to tap water no mater how long it stands or what you put into it.
There are other opionions on this subject but if it were not for KIP, I would be back to watching the fish swim and corals at my LFS and not in my own living room.
He saved my tank by telling me not to use tap water and by the Gods he was sooo right.
Since I have been using RO/DI water my tank looks wonderful and there is no bad algae, I did not even get the green hair algae that is bad.
Just look at a tank with tap and then look at one with RO/DI water. You will know what I mean.
I am so happy with the advise this man gave. Thank you Kip and I will miss you.
Here is the proof in my tank. so PLEASE do youself and your fish and corals a favor, use RO/DI water.