During maintenance I noticed a significant amount of beach sand in the evaporator coil pan. Home is on the intercoastal with a very low return grill. I performed a chemical cleaning one section at a time due to the corrosion on the coil fins. Used dropcloth to line the inside of return box. Shop vac on drain line during cleaning. Wipe down air handler interior after rinsing chemical away. Reconnected drain line to condensate pump. Reinstalled filter. Gave a recommendation for corrosion grenade for the indoor and outdoor units for a second time due to lots of evidence of corrosion on the coils. Brought this to the customers attention.