Quoting from the article "Fish Waste and Macrophytes" of BarrReport:
"NH3/NH4, rather than NO3 and PO4, are the causative environmental factors that lead to algae blooms when more CO2 and light are added."
"Adding PO4 and NO3 using inorganic salts on non CO2 lower light systems has not been shown to induce algae. Varying CO2, disturbing the sediments, adding urea or too many fish, adding NH4 and increasing the light has been shown to induce algae in these non CO2 systems."
I would recommend reading through the articles "Nitrogen Cycling in Planted Aquariums" and "Fish Waste and Macrophytes" of BarrReport, as a start, in order to understand the mentioned dynamics even further.