Depending on the size of the res you mix up in, you can use an airline and stone. I saw one guy (commercial grower, mixing up 100L) use a submersible pump as a mixer
I also use the GH trio, but I dont see white in the res. On the outside, sure (spilled nutes dry and leave salt stains)
I do get sediments (I blame the micro, it always seems gritty)
And ya, change your order of nutes, like FDP mentioned