cleaning Aluminum Radiator?

[mod5v]

I think some of my heating problems could be an inefficiant radiator. It was used when i got it a 28" double pass. inside it looks a little brownish like it may have some calcium build up. just wondering what I should use to clean it with. I tried purple power but didnt do anything. Would muratic acid be to strong? Any advice?

 

[jos51700]

Calcium Lime Rust "CLR" remover maybe?

 

[70Duster440]

Dumping some vinegar in should dissolve calcium too.