Plants seem to have insect problem

Woke up this morning and uhhhh.....Noooooooo I think theres spider mites in my soil.And near stock.Went to the hydro store got 3in1 safer brand.Its OMRI listed.Used a little but not sure how much to use.Contains sulfur and scared of the plants getting sulfur burn,and build up.Not all plants have mites.Should I spray the plants that didn't have mites visible?Just to mention crops indoor.Thank You!PLEASE HELP!!!

If I were you I would spray the plants that have no insect in them to prevent it from having any.