With out a test kit you are basically blind.Well besides what the fish can tell you ,combined with BASIC knowledge.
One fish is telling you something is up...
You say ;He is new to the tank (about a week) along with some other of his kind that have been fine.
How many did you add?
Change water since you don't have a kit.
You added to you filter load along with stocking so you need to help the BB grow.
TB are mean(MEAN) fish ...How big is your tank and how many TB?
Change water !