Fortinet Firewall best way to monitor bandwidth?

Greetings 

I'm seeking an alternative for a MRTG for the fortigate 200e . Experiencing issues where as we are exceeding the bandwidth provided by our ISP an I would like to know the best way to monitor the bandwidth to see where its being used the most (Solarwinds was my first thought but would like to know if anyone else have another solution )

Thanks