You didn't say what type of ...

You didn't say what type of body of water this is? Regarding "shade Balls" white balls works better than black balls which enhance solar thermal heating and contribute to evaporation. "shade balls" are mostly used to keep water fowl out of reservoirs eliminating droppings that could contaminate the water with avian-borne pathogens. If it is a reservoir then surface agitation to change the Richardson's Index would help retard evaporation. Eliminating the thermal stratification (thermocline) is also a good technique, i.e. bringing colder hypolimnion water to the surface to lower temperature and make it more uniform aids in retarding evaporation while increasing the overall water quality.