I'm sure you are rinsing the sand REALLY well. Surfactents tend to leave a filmy residue. Plain white vinegar will cut the film. Also, if there is a little residual vinegar, it will not harm the bioload. Personally, I would be extremely cautious with the bleach. A solution of 19:1 would limit any problems you may have and the dechlorinator will take care of it. It could have been worse.