Algae accumulates nutrients in its tissues and after die off may release it back to the water. Also, after the lights goes off, photosynthesis stops and algae start producing the CO2, which will lower PH in your system. You can add herbovour animals like turbo/astraea snails, Lawmower blenny.
Tap water has another bad characteristic. Except clorine and chloramine it may contain heavy metals, other toxic components. Which can cause a lot of problems in your tank.