How to Control Algae in Gar Tank??

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Guys lately algae starting to develop in my tank, i have to rub every 3 day in the front glass and it makes the water cloudy after i rub it.. plecos and flagtail would be nice addition but too bad i don't dare to risk adding them to my gar tank.. is there any other alternatives to get rid of the algae in your gar tank?

thanks in advance