Those big holes are not spider mites. they may have helped.
When you say tap water what do you mean ? well ? city,county ?
I ask because how much poisin is too much. I know soil is much more forgiving than hydro but in a container is similar.
Save your self some problems and get distilled or R/O water and add only what you want to it.
no guessing, you know.

by the way it looks like some kind of chlorine or iron problem. mighty wash is the stuff for mites and if you spray it in your face you want even get sick like azamax poisined me.