Tiger Barb isolating himself and not eating
About a week ago I changed over my tiger barb tank from a 20 tall to a 20 long. Since then, one of the larger males has generaly been staying in one spot. His color is bright and has no nipped fins, but he is not interested in food at all and hasn't eaten in 3 or 4 days. He will occasionally swim a lap around the tank, but keeps his fins flared. I have not noticed any bullying towards him at all.
Water quality is fine, 0 ammonia and nitrite, nitrate never above 20. Its moderately planted, and has lots of hiding spots.
The rest of the fish are fine, I first assumed stress, but its been a week now and he has not changed.
My ph is also very high out of the tap, at 8.2., but they have been fine with it for 3 months.
Any advice or ideas?