Kanaplex
 

Is your tang eating. I suggest you soak his food in the medication, feed him and dose in your qt for the full dose but with only 1/5 the water for 5-10 minutes then fill the qt up the rest of the way so that it’s a regular dosage. Do this daily if you can in a 5 gallon bucket. Watch the ammonia levels. I use chemstars from my main tank and add to a filter in the bucket.

Good luck and do not treat beyond the recommended days of dosage.