Tap water usually has lotsa silicates and stuff in it that help promote that. Eventually you might even run into cyanobacterial blooms and really yuck stuff like that with tap water (maybe).
It does help to set up an RO
filter (the DI
or deionization resin on the tail end of the filter assembly really helps) and use this water for all salt mix and water changes, and then you could also get extra snails, and algae blennies love to eat that stuff too.