Bottled water still doesn't mean it's good water. Find out how they are filtering it if you can. Most water companies use only ro filtration. Which still leaves you with possible phosphates.

Also what and how are you feeding your stock? What is your lighting schedule? These are all contributing factors in algae growth. Check you Nitrate levels.

Just so ya know I've been keeping SW for just a little over 2yrs. The tank I have running now is just shy of 6 months old and still considered very new. I just got done with a battle of turf algae and before that it was major diatoms. I'm sharing what I've learned from others here and from personal experience with the same issues you are now having. Be patient with yourself and especially your tank. Nothing good will come from a quick fix.