Snapshot autodelete for root volumes?

Greetings,

My question is to address all the "snapshot reserve 90%" full alerts we're getting from unified manager. This seems to be an issue in every site.

These root volumes don't seem to have autodelete turned on but they are still within the default 5% reserve space, just nearly full. They have the default policy applied 2 weekly, 6 daily and 6 hourly or whatever it is.

I didn't want to go making changes to the root volumes and aggregates everywhere without knowing what the best practices are. 

Can anyone advise me on how to keep the snapshot reserve below 90%?

Thanks in advance