Are you adjusting up or down? And what pH-adjuster are you using?

I'm pretty sure it's when I bring the ph up when I first make up some fresh solution. When I add the PH up (Potassium Hydroxide) it goes cloudy before I give it a good mix. I use Acetic acid 75% to bring it down.

Cheers

Fil

Yeah,
In that case you're right that its either calcium or magnesium.(probably magnesium)

MMM, so is this what normally happens? If it is calcium or magnesium this could pose as a problem when growing heavy feeders like tomato's.

Fil

No problem. Particularly since the cloudiness goes away after stirring.
I'm sure its just temporary magnesium hydroxide (highly insoluble) forming as you add the potassium hydroxide.
Try and dilute the KOH more before you add it.