Suggestions on removing mildew off flagstone?

[boohicks]

Our spa is 12 in high and underneathe the rim of flastone on the outside of the spa, on the flagstone is mildew I think. Hoping not mold? Any ideas on what to use to get rid of it? Tried power washing and it did nothing! Thanks

 

[axell]

Try some dilute bleach solution and a brush, if that does not work, up the % of bleach.

 

[Renron]

Simple Green works Great!
Ron