When I do single buckets I put my water in a spare bucket throw a air stone in it, add my big bloom wait 12-24 hours add grow big , wait 12- 24 add h2o2 , wait 12-24 add calmag, wait 12-24 add pH up or down to 5.7 . If I'm doing 6 bucket rdwc I'll use this to top off the res once a week or for res changes. Any other top offs will be with water , calmag , h2o2 conditioned for 24 hours.
Thing is I was struggling with pH swing until a member offered me some advice , and almost instantly fixed my issues . See what was happening was the calcium was falling out. And he recommended switching my pH down to a sulfuric acid based , and conditioning the brew . It worked perfectly .