Is there something different about this tank when compared to your other tanks that dont have this issue? Perhaps its heavily stocked or has sand? I am not an expert on algae issues but I believe an excess of silicates (such as from silica sand or your tap), phosphates or nitrates are all contributing factors. If your tap water was to blame, you would have this issue in all of your tanks so you will need to figure out whats different about this tank when compared to your others. Hopefully, someone with a bit more experience on this topic can ID what the exact issue here is!