Just went over the booklet for it again the range is 0 to 2.50ppm NH3 so im litterally at the limit of it. Not sure why the checker even says NH4 on it bc I can't test either orI wouldnt add to your display or change water in it if you're interested in doing the symptoms test. just let it ride until tuesday and put one fish in it, chart for a few hours, if he's normal then that tank carries fish like all the patterns we see. and if he is in poison water, his behavior will indicate that in obvious ways, not just swimming directly in a corner or something. he'll flop and die if burned.
the fact your device reads .1 in fresh mixed water, where the lethal range is .05 in most circles of analysis-that is a stat oulier because its coming from no test load water and still stating alarm/concern ammonia.
(hey have you verified all settings and procedures on the device itself are correct? are there any calibration steps to take, or can you select between nh4 and nh3??)
that still leads towards test issues, there are no known reef salts that mix up lethal amounts of nh3, not any. not ever.
there's some ammonia in reef salts going off the totality of Randy's posts and writeups, but not .1 nh3 / nope/ none of them mix to that level is my firm bet.