even using tap water just to top off can be a big problem with that since micro algae thrive on even a little added phosphates and other nutrients i have noticed. all of these are added to a municipal water supply specifically phosphorous to help take care of people with older piping. that in turn enters your system when you add it to any degree.
for a while i had "green water" where the water itself was actually green. it hasn't gone away totally but has died down quite a lot since i started using distilled water and now that i have added a phosphate eliminator in my HOB
filter it and put the skimmer on full (pulling all kinds of green gunk out) and this week i am reducing the lighting to 5-6.5 hours a day and i think i am noticing it start to get even better. so there ya have it.