Hoover the hood. Powerwash (some people say dont do this but i have without any problems)
Use a proper hood leaning kit with shampoo and waterproofing spray. You may need to shampoo 2 or three times. Use a small brush to get into the folds of the fabric. The fabric is pretty tough and can take some agitation by a brush or sponge to shift the deep down dirt.
my previous hood had oily hand prints(thanks to a guy in garage)the foam spray thing in one of these foreigners hand washes got that off,so I wouldn't worry about algae too much,should be easily removed !