OK, cool. I cleaned the inside of the tank thoroughly before I planted everything... there was hard green spot algae on the glass, so maybe I'm already lacking phosphates. Actually, the tap water shouldn't have any at all, that's supposed to be one of the things removed by the water conditioner.
Our city water sucks... bad. The reservoir is a lake, and they allow power boats on the lake... so we have traces of petroleum type chemicals in the water... A bit of trichlorethylene and tetrachlorethylene goes a long ways.... (If I remembered the chems right...) But they say it's a safe level....