Tap water is an unkown until you do some research & find out what's in it. Will definitely affect the operation of your system long term. Very few of us are fortunate to have pure enough tap water or tap water with all the 'right' ingredients to successfully run a tank for the long haul. The folks around Greater Vancouver have tap water TDS of less than 20, my source in Vernon is 210+. Good place to start is with a water quality report from your local utility.
http://www.devon.ca/Government/Depar...erUtility.aspx
I used treated tap water for just over a year & things did ok, but never looked that great & always a struggle with outbreaks of various undesireable stuff. Some of it we deal with regardless when starting a new tank (part of cycling the system), but I've been using RODI water now for years & things have never looked better. Lights can also affect what type of algae takes hold. The blue spectrum will suppress most types of green algae.