Oase pontec pondopress filter

Roughly 8-10k litre pond full sun, 55w UV, constantly getting string algae but my filter is only for around 10k litre pond without fish, think it’s oase pontec pondopress. Obviously looking to upgrade as it’s well undersized but are these worth the money or should I be looking elsewhere? And will a bigger filter help with string algae or going to have to add shade?