I made a small container of sodium carbonate from baking soda probably 5 years ago and have used it a couple times to make a small bottle of electrolyte and my Colloidal Silver has been as clear now as it was the day I made the sodium carbonate and my first batch of electrolyte.
As Kephra suggest, food grade could have contaminants. USP grade which is what baking soda is (at least Arm and Hammer brand), by virtue of the rating must be VERY pure (thats pharmaceutical/drug grade).
Perhaps try making some of your own carbonate from bicarb and see what happens.