Question about PH DOWN

Currently on week 4 veg in PROMIX HP. I PH'd distilled tap water/calmag down to 6.1 from 7.3

Was wondering if I'm able to PH DOWN a second time after my leftover mixture has been sitting for 3 or 4 days or is it best to just dump it & mix up a new batch when the time comes?

Can I PH DOWN a second time 6 to 8 days after mixing up a full feed if I still have some leftover?

If it's just calmag and water in soil there is no need to ph it down....in soil grows I don't ph anything.
My tap is around mid 7's and that's how I use it.