Black brush algae..excess phosphates?

Dick wrote in
:

160 watts over 55 gallons is almost 3 watts per gallon. I use 1.5 w/g
or lower as the definition of "low light." I don't know what happens
when low light plants are exposed to "high light" conditions. Could
this be a problem?

Yes. Excessive light will damage low light plants and cause algae
problems.

If your tank is extremely low in macro-nutrients you may not see much algae
from excessive light, but the light still may still burn out the
chloroplastid cells and shock or just dwarf the plant.

Even bright light plants may become overrun with algae if it isn't balanced
off with sufficient CO2.

Anubias and Madagascan lace (Aponogeton madagascariensis) are prime
examples of plants that don't fair well and/or become overrun with algae
under very bright direct light.