Foot felt a bit painful and i discovered i have a blood blister on the ball of the foot. whats the best way to treat it a blister plaster?

See below: Soak in warm water with epsom salt, apply antiseptic and bandaid.

Protect it: An unpopped blister represents a closed sterile environment. Yes on occasion one can become infected then it is time to open it, however the risk of infection in a dressed open wound is still higher than that of an intact blister. The blister will gradually resolve with time.