It's not recommended to use algae cleaner at all. If the tank is cleaned regularly and has minimal algae spots in it, manual spot cleaning with a toothbrush or an algae scraper is an effective way to remove the spots. If the tank has a lot of algae spots due to infrequency between cleaning, consider increasing how regular the tank is cleaned.
Algae cleaners can be harmful to the fish and other inhabitants of the aquarium, as well as to the beneficial bacteria that live in the filter. If algae becomes a problem, it is best to try to remove it by reducing the amount of light the tank receives, increasing the water circulation, and/or adding some algae-eating fish or invertebrates.