The algae appears when the NH4 waste is not being taken up by the
plants.
The plants might not take it up because of the missing nutrients which
slow the plant's abilty to uptake nutrients like NH4 in particular or
NO3.

NH4 will certainly cause this algae to appear if enough is present for
a few days/hours. Adding more fish or reducing plant mass too much can
cause this increase in NH4. When you cycle your tank it often gets
algae for this reason, since the plants are getting established along
with the bacteria. These two keep the NH4 down and algae as a result.

Regards,
Tom Barr