So i am in no ways an expert on aquariums. But when i visit my grandma her aquarium always looks like this and i dont get it… she told me she cleans it every week (stones and decoration) but the algae growth is insane. Now this tank is for simple fish (mainly guppies) but i dont think she either needs a more powerful filter or maybe some plants? Also dont mind the creepy face its just an old finding nemo decoration. Also for your information the algae seems too be very liquid-ish not like clumped up together river algae.