I would worry about just getting the salinity right, add the sand. If you are starting the cycle, pH will fluctuate, so I wouldn't worry at this point.
I use a 43G plastic bucket to premix my water.
This is my schedule:
Friday-add water, salt, ph, and heater
Saturday-test salinity, add salt/water, if needed (count how many scoups of salt you put in the water), you will know how much to add after a few times.
Sunday-remove old SW
, clean my equipment (in the old SW
) and add the new water to the tank.