HELP!! Possible ich on fish?

[bsung413]

I have a bicolor blenny in my tank for about 2 months now, just two weeks ago I notices that he will sometime scratch on rock, but I am not seeing any visible white spot on him

He is still eating like a pig! I mean it, he eats alot! His tank mate are pipefish, mandarin, twin spot goby, and many inverts ( shrimps and crab).
There are 2 anemone ( RBTA, GBTA), green open brain, and 2 gorgonian.

Tank parameter
Ammonia :0
Nitrate :0
Nitrite :0
Phosphate :0-0.25
PH: 8.0

10% WC every weeks, 25% every 2 months.

This start happening after I added a sand sifting goby (twin spot) and my tank got little cloudy for a few days but now is cleaned up but the blenny is still scratching!

Any idea why is he doing that? Could it be ich or anything that is irritating him?