i got a whole bunch of chemicals and salts to put in my pool, should i put them in knowing that is is supposed to rain? or wait until the forecast calls for a clear day? does rain water affect the pools balance that much?

i got a whole bunch of chemicals and salts to put in my pool, should i put them in knowing that is is supposed to rain? or wait until the forecast calls for a clear day? does rain water affect the pools balance that much?