Hmm. i use this salt.. but have never encountered yellowish water... even thou i use tap water and mix the salt with a pump.. the water clears up within an hour upon mixing..
Do u use tap water for mixing? then that may be the source of NO3 and PO4 which u positively tested.
Resized your pic
(anyway the water doesn't look yellow from my screen.. maybe its cos of my lousy LCD monitor )