How do you clean stubborn algae off equipment?

Hi Guys

Just a quick question, I'm starting up second-hand a tank that was donated by a friend. Although I'm very grateful, some the equipment, especially the hang on the back filter and heater have some some very stubborn, almost concrete like algae patches. I have tried simple dish soap and hot water but its still incredibly difficult to clean.
I'm asking you guys, is there any particular trick that I can use? Lemon juice or vinegar and bicarb? Because literally scrubbing firmly with a nail brush and it doesn't budge

Thanks in advance
Matt

 

Vinigar or citric acid (the green packet) and an good soak.

 

Thank you, it worked!