No adding lime will not hurt. I you have a tannic acid look it more than likely does indeed have a low alkalinity and pH. To answer your original question spreading it all over the pond surface is best, but putting in as many places as possible will help. ALso the amount of time it works keeping the alkalinity above 20 ppm depends on water flow, 4 tons/acre may only be good for 3 years with a low retention time.

Greg Grimes
www.lakework.com