Niger trigger help

ive had my niger for about 3 1/2 yrs. the last 3 weeks or so he has not been eating and acting as if he has lost sence of smell/sight bumping into everything if he comes out of the rocks at all. most of the time he is wedged in the rocks. he looks healthy eyes are clear coloring is normal but he is now starting to get a little thin. tank mates are yellow tang 3 damsels a clown and a purple pseudo. no new fish in over a yr. tank size is 240 salt is 1.024 ph 8.0 (low i know just added buffer) ammonia 0.25 trites 0 trates between 0-5.0 temp 76-78
any info would be great thanks
 
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