It could be the sulfates in your jack's combining with the calcium in your tap water and forming gypsum. If your sulfates are not diluted enough this will happen. Just a guess though.
this is happening immediately upon adding the jack's with no time delay so it has not had the time to form a precipitate. everything goes into solution fast except for this stuff, which settles to the bottom and slowly dissolves. in ro water it all almost goes into solution but in tap there is a higher percentage of it left over.
it acts just like straight mag sulfate, slow to dissolve.
i mix into the full amount of water, stir it in and let it set about ten minutes, stir again and then add the calcinit.
it doesn't seem to affect anything.