(Don’t mind the message😁 )Been thinking of options so it doesn’t need power washed every month
algae -- have to keep it dry! is it at ground level where water accumulates after a rain ?? Clean it ( pressure wash! again!), get it BONE BONE dry ( if you can ) then use an outdoor concrete sealer ... Seal-Krete makes a good product .. but prep is everything!
You'll probably need some form of fungicide to keep the mold from coming back. You also should reroute any water that is getting to the area from down spouts or A/C condensation. If you can keep the area dry you are halfway home.
Try Never Wet. It makes water roll of of things. Use several coats after you have thoroughly cleaned and let dry.
Use bleach water. Will kill mold