I just put up our new pool. It is the 18' x 9' x 52" with an Intex SWG and a 1,600gh sand filter. How do I go about starting? It is almost 5,000 gallons but isn't completely filled yet. The directions said I would need 3- 40 lb bags of salt to start with. Is that all I need to initially start? What else am I missing?