This depends on the kind of weather and
environment you are living in. If you live more than 10kms away from a
beachfront or a sheltered bay, your screens can be cleaned every 6 months. If
you live 500m to 1km away from the beach, then have it cleaned every month.
Lastly, your screens should be cleaned once every 2 weeks if you live less than
500m from a sheltered bay or beachfront.