I suspect the JBL test strip are giving you a false positive. I wonder if the colour is simply being read differently from 4 weeks ago because its starting to be darker in the evenings.
I have tried those strips twice on the same sample and got different numbers. I have used them to "check" the results of liquid tests. From what I've measured 0.25 nitrite on that strip probably corresponds to zero true value. In addition as I understand things nitrite spikes don't really happen unless the tank is still cycling, though you may get ammonia spikes if you overload system.
I would also estimate that the 25 nitrate is closer to 10 real number. In situations where you are worried about water quality being different to normal an ammonia test will be the most help.
Keep monitoring the fish to see if he/she heals, I think the water is fine.
Regardless you might want to do a water change anyway just in case the strip is wrong the other way than what I think. In addition a water change will dilute any germs in the water that might cause the wound healing some problems.
As for medications - I have little experience in using these - but someone mentioned things with mela in the name are bad for Betta, so therefore also to Gourami who are related. I don't know whether or not aquarium salt treatment would help or be harmful. Clean water is usually the best medicine,
. I was told they would be fine in my tank set up 
